{"appState":{"pageLoadApiCallsStatus":true},"articleState":{"article":{"headers":{"creationTime":"2016-03-26T11:01:58+00:00","modifiedTime":"2016-04-25T19:47:03+00:00","timestamp":"2022-09-14T18:14:25+00:00"},"data":{"breadcrumbs":[{"name":"Academics & The Arts","_links":{"self":"https://dummies-api.dummies.com/v2/categories/33662"},"slug":"academics-the-arts","categoryId":33662},{"name":"Math","_links":{"self":"https://dummies-api.dummies.com/v2/categories/33720"},"slug":"math","categoryId":33720},{"name":"Basic Math","_links":{"self":"https://dummies-api.dummies.com/v2/categories/33722"},"slug":"basic-math","categoryId":33722}],"title":"How to Measure Triangles","strippedTitle":"how to measure triangles","slug":"how-to-measure-triangles","canonicalUrl":"","seo":{"metaDescription":"You can measure the perimeter and area of all triangles. There also is a special feature of right triangles that allows you to measure them more easily. Finding","noIndex":0,"noFollow":0},"content":"You can measure the perimeter and area of all triangles. There also is a special feature of right triangles that allows you to measure them more easily.\r\n<h2 id=\"tab1\" >Finding the perimeter and area of a triangle</h2>\r\nMathematicians have no special formula for finding the perimeter of a triangle — they just add up the lengths of the sides.\r\n\r\nTo find the area of a triangle, you need to know the length of one side — the <i>base</i> (<i>b</i> for short) — and the <i>height</i><i> </i><i>(h).</i> Note that the<i> </i>height forms a right angle with the base. This figure shows a triangle with a base of 5 cm and a height of 2 cm:\r\n\r\n<img src=\"https://www.dummies.com/wp-content/uploads/437204.image0.jpg\" alt=\"image0.jpg\" width=\"455\" height=\"202\" />\r\n\r\nHere's the formula for the area of a triangle:\r\n\r\n<img src=\"https://www.dummies.com/wp-content/uploads/437205.image1.jpg\" alt=\"image1.jpg\" width=\"138\" height=\"57\" />\r\n\r\nSo here's how to figure out the area of a triangle with a base of 5 cm and a height of 2 cm:\r\n\r\n<img src=\"https://www.dummies.com/wp-content/uploads/437206.image2.jpg\" alt=\"image2.jpg\" width=\"449\" height=\"57\" />\r\n<h2 id=\"tab2\" >Finding the third side of a right triangle</h2>\r\nThe long side of a right triangle <i>(c)</i> is called the hypotenuse, and the two short sides (<i>a</i> and <i>b</i>) are called the <i>legs</i>:\r\n\r\n<img src=\"https://www.dummies.com/wp-content/uploads/437207.image3.jpg\" alt=\"image3.jpg\" width=\"379\" height=\"293\" />\r\n\r\nThe most important right triangle formula is the <i>Pythagorean theorem</i>:\r\n\r\n<img src=\"https://www.dummies.com/wp-content/uploads/437208.image4.jpg\" alt=\"image4.jpg\" width=\"130\" height=\"33\" />\r\n\r\nThis formula allows you to find the hypotenuse of a triangle, given only the lengths of the legs. For example, suppose the legs of a triangle are 3 and 4 units. Here's how to use the Pythagorean theorem to find the length of the hypotenuse:\r\n\r\n<img src=\"https://www.dummies.com/wp-content/uploads/437209.image5.jpg\" alt=\"image5.jpg\" width=\"129\" height=\"120\" />\r\n\r\nSo when you multiply <i>c</i> by itself, the result is 25. Therefore, take the square root of both sides to find:\r\n<blockquote><i>c</i> = 5</blockquote>\r\nThe length of the hypotenuse is 5 units.","description":"You can measure the perimeter and area of all triangles. There also is a special feature of right triangles that allows you to measure them more easily.\r\n<h2 id=\"tab1\" >Finding the perimeter and area of a triangle</h2>\r\nMathematicians have no special formula for finding the perimeter of a triangle — they just add up the lengths of the sides.\r\n\r\nTo find the area of a triangle, you need to know the length of one side — the <i>base</i> (<i>b</i> for short) — and the <i>height</i><i> </i><i>(h).</i> Note that the<i> </i>height forms a right angle with the base. This figure shows a triangle with a base of 5 cm and a height of 2 cm:\r\n\r\n<img src=\"https://www.dummies.com/wp-content/uploads/437204.image0.jpg\" alt=\"image0.jpg\" width=\"455\" height=\"202\" />\r\n\r\nHere's the formula for the area of a triangle:\r\n\r\n<img src=\"https://www.dummies.com/wp-content/uploads/437205.image1.jpg\" alt=\"image1.jpg\" width=\"138\" height=\"57\" />\r\n\r\nSo here's how to figure out the area of a triangle with a base of 5 cm and a height of 2 cm:\r\n\r\n<img src=\"https://www.dummies.com/wp-content/uploads/437206.image2.jpg\" alt=\"image2.jpg\" width=\"449\" height=\"57\" />\r\n<h2 id=\"tab2\" >Finding the third side of a right triangle</h2>\r\nThe long side of a right triangle <i>(c)</i> is called the hypotenuse, and the two short sides (<i>a</i> and <i>b</i>) are called the <i>legs</i>:\r\n\r\n<img src=\"https://www.dummies.com/wp-content/uploads/437207.image3.jpg\" alt=\"image3.jpg\" width=\"379\" height=\"293\" />\r\n\r\nThe most important right triangle formula is the <i>Pythagorean theorem</i>:\r\n\r\n<img src=\"https://www.dummies.com/wp-content/uploads/437208.image4.jpg\" alt=\"image4.jpg\" width=\"130\" height=\"33\" />\r\n\r\nThis formula allows you to find the hypotenuse of a triangle, given only the lengths of the legs. For example, suppose the legs of a triangle are 3 and 4 units. Here's how to use the Pythagorean theorem to find the length of the hypotenuse:\r\n\r\n<img src=\"https://www.dummies.com/wp-content/uploads/437209.image5.jpg\" alt=\"image5.jpg\" width=\"129\" height=\"120\" />\r\n\r\nSo when you multiply <i>c</i> by itself, the result is 25. Therefore, take the square root of both sides to find:\r\n<blockquote><i>c</i> = 5</blockquote>\r\nThe length of the hypotenuse is 5 units.","blurb":"","authors":[{"authorId":9399,"name":"Mark Zegarelli","slug":"mark-zegarelli","description":" <b>Mark Zegarelli</b> is a professional writer with degrees in both English and Math from Rutgers University. He has earned his living for many years writing vast quantities of logic puzzles, a hefty chunk of software documentation, and the occasional book or film review. Along the way, he’s also paid a few bills doing housecleaning, decorative painting, and (for ten hours) retail sales. He likes writing best, though.","hasArticle":false,"_links":{"self":"https://dummies-api.dummies.com/v2/authors/9399"}}],"primaryCategoryTaxonomy":{"categoryId":33722,"title":"Basic Math","slug":"basic-math","_links":{"self":"https://dummies-api.dummies.com/v2/categories/33722"}},"secondaryCategoryTaxonomy":{"categoryId":33726,"title":"Pre-Algebra","slug":"pre-algebra","_links":{"self":"https://dummies-api.dummies.com/v2/categories/33726"}},"tertiaryCategoryTaxonomy":{"categoryId":0,"title":null,"slug":null,"_links":null},"trendingArticles":[{"articleId":172026,"title":"Repurposing Items for Beautiful Holiday Decorating","slug":"decorating-for-the-holidays-with-what-you-already-have","categoryList":["home-auto-hobbies","crafts","gifts-holidays"],"_links":{"self":"/articles/172026"}},{"articleId":192609,"title":"How to Pray the Rosary: A Comprehensive Guide","slug":"how-to-pray-the-rosary","categoryList":["body-mind-spirit","religion-spirituality","christianity","catholicism"],"_links":{"self":"/articles/192609"}},{"articleId":193770,"title":"How to Play Rummy: All You Need to Know","slug":"rummy-understanding-the-rules-and-starting-a-game","categoryList":["home-auto-hobbies","games","card-games","general-card-games"],"_links":{"self":"/articles/193770"}},{"articleId":153792,"title":"Format Numbers in Thousands and Millions in Excel Reports","slug":"format-numbers-in-thousands-and-millions-in-excel-reports","categoryList":["technology","software","microsoft-products","excel"],"_links":{"self":"/articles/153792"}},{"articleId":147241,"title":"How to Use the Z-Table","slug":"how-to-use-the-z-table","categoryList":["academics-the-arts","math","statistics"],"_links":{"self":"/articles/147241"}}],"inThisArticle":[{"label":"Finding the perimeter and area of a triangle","target":"#tab1"},{"label":"Finding the third side of a right triangle","target":"#tab2"}],"relatedArticles":{"fromBook":[{"articleId":194384,"title":"How to Write Numbers in Scientific Notation","slug":"how-to-write-numbers-in-scientific-notation","categoryList":["academics-the-arts","math","algebra"],"_links":{"self":"https://dummies-api.dummies.com/v2/articles/194384"}},{"articleId":158569,"title":"Inverse Operations and Commutative, Associative, and Distributive Properties","slug":"inverse-operations-and-commutative-associative-and-distributive-properties","categoryList":["academics-the-arts","math","basic-math"],"_links":{"self":"https://dummies-api.dummies.com/v2/articles/158569"}},{"articleId":158567,"title":"Converting Metric Units to English Units","slug":"converting-metric-units-to-english-units","categoryList":["academics-the-arts","math","basic-math"],"_links":{"self":"https://dummies-api.dummies.com/v2/articles/158567"}},{"articleId":158560,"title":"A Guide to Working with Exponents, Radicals, and Absolute Value","slug":"a-guide-to-working-with-exponents-radicals-and-absolute-value","categoryList":["academics-the-arts","math","basic-math"],"_links":{"self":"https://dummies-api.dummies.com/v2/articles/158560"}},{"articleId":158557,"title":"A Quick Conversion Guide for Fractions, Decimals, and Percents","slug":"a-quick-conversion-guide-for-fractions-decimals-and-percents","categoryList":["academics-the-arts","math","basic-math"],"_links":{"self":"https://dummies-api.dummies.com/v2/articles/158557"}}],"fromCategory":[{"articleId":291491,"title":"Teaching Your Kids New Math (K-5) For Dummies Cheat Sheet","slug":"teaching-your-kids-new-math-k-5-for-dummies-cheat-sheet","categoryList":["academics-the-arts","math","basic-math"],"_links":{"self":"https://dummies-api.dummies.com/v2/articles/291491"}},{"articleId":253710,"title":"Pre-Algebra Practice Questions: Comparing Fractions Using Cross-Multiplication","slug":"pre-algebra-practice-questions-comparing-fractions-using-cross-multiplication","categoryList":["academics-the-arts","math","basic-math"],"_links":{"self":"https://dummies-api.dummies.com/v2/articles/253710"}},{"articleId":249996,"title":"Pre-Algebra Practice Questions: Solving Simple Algebraic Equations","slug":"pre-algebra-practice-questions-solving-simple-algebraic-equations","categoryList":["academics-the-arts","math","basic-math"],"_links":{"self":"https://dummies-api.dummies.com/v2/articles/249996"}},{"articleId":249986,"title":"Pre-Algebra Practice Questions: Isolating x in an Equation","slug":"pre-algebra-practice-questions-isolating-x-equation","categoryList":["academics-the-arts","math","basic-math"],"_links":{"self":"https://dummies-api.dummies.com/v2/articles/249986"}},{"articleId":249980,"title":"Pre-Algebra Practice Questions: Rearranging Equations to Isolate x","slug":"pre-algebra-practice-questions-rearranging-equations-isolate-x","categoryList":["academics-the-arts","math","basic-math"],"_links":{"self":"https://dummies-api.dummies.com/v2/articles/249980"}}]},"hasRelatedBookFromSearch":false,"relatedBook":{"bookId":281978,"slug":"basic-math-pre-algebra-for-dummies-2nd-edition","isbn":"9781119293637","categoryList":["academics-the-arts","math","basic-math"],"amazon":{"default":"https://www.amazon.com/gp/product/1119293634/ref=as_li_tl?ie=UTF8&tag=wiley01-20","ca":"https://www.amazon.ca/gp/product/1119293634/ref=as_li_tl?ie=UTF8&tag=wiley01-20","indigo_ca":"http://www.tkqlhce.com/click-9208661-13710633?url=https://www.chapters.indigo.ca/en-ca/books/product/1119293634-item.html&cjsku=978111945484","gb":"https://www.amazon.co.uk/gp/product/1119293634/ref=as_li_tl?ie=UTF8&tag=wiley01-20","de":"https://www.amazon.de/gp/product/1119293634/ref=as_li_tl?ie=UTF8&tag=wiley01-20"},"image":{"src":"https://www.dummies.com/wp-content/uploads/basic-math-and-pre-algebra-for-dummies-2nd-edition-cover-9781119293637-203x255.jpg","width":203,"height":255},"title":"Basic Math & Pre-Algebra For Dummies","testBankPinActivationLink":"","bookOutOfPrint":true,"authorsInfo":"<p><b><b data-author-id=\"9399\">Mark Zegarelli</b></b> is a professional writer with degrees in both English and Math from Rutgers University. He has earned his living for many years writing vast quantities of logic puzzles, a hefty chunk of software documentation, and the occasional book or film review. Along the way, he’s also paid a few bills doing housecleaning, decorative painting, and (for ten hours) retail sales. He likes writing best, though.</p>","authors":[{"authorId":9399,"name":"Mark Zegarelli","slug":"mark-zegarelli","description":" <b>Mark Zegarelli</b> is a professional writer with degrees in both English and Math from Rutgers University. He has earned his living for many years writing vast quantities of logic puzzles, a hefty chunk of software documentation, and the occasional book or film review. Along the way, he’s also paid a few bills doing housecleaning, decorative painting, and (for ten hours) retail sales. He likes writing best, though.","hasArticle":false,"_links":{"self":"https://dummies-api.dummies.com/v2/authors/9399"}}],"_links":{"self":"https://dummies-api.dummies.com/v2/books/"}},"collections":[],"articleAds":{"footerAd":"<div class=\"du-ad-region row\" id=\"article_page_adhesion_ad\"><div class=\"du-ad-unit col-md-12\" data-slot-id=\"article_page_adhesion_ad\" data-refreshed=\"false\" \r\n data-target = \"[{"key":"cat","values":["academics-the-arts","math","basic-math"]},{"key":"isbn","values":["9781119293637"]}]\" id=\"du-slot-63221a012f8f2\"></div></div>","rightAd":"<div class=\"du-ad-region row\" id=\"article_page_right_ad\"><div class=\"du-ad-unit col-md-12\" data-slot-id=\"article_page_right_ad\" data-refreshed=\"false\" \r\n data-target = \"[{"key":"cat","values":["academics-the-arts","math","basic-math"]},{"key":"isbn","values":["9781119293637"]}]\" id=\"du-slot-63221a012feca\"></div></div>"},"articleType":{"articleType":"Articles","articleList":null,"content":null,"videoInfo":{"videoId":null,"name":null,"accountId":null,"playerId":null,"thumbnailUrl":null,"description":null,"uploadDate":null}},"sponsorship":{"sponsorshipPage":false,"backgroundImage":{"src":null,"width":0,"height":0},"brandingLine":"","brandingLink":"","brandingLogo":{"src":null,"width":0,"height":0},"sponsorAd":"","sponsorEbookTitle":"","sponsorEbookLink":"","sponsorEbookImage":{"src":null,"width":0,"height":0}},"primaryLearningPath":"Advance","lifeExpectancy":null,"lifeExpectancySetFrom":null,"dummiesForKids":"no","sponsoredContent":"no","adInfo":"","adPairKey":[]},"status":"publish","visibility":"public","articleId":149990},"articleLoadedStatus":"success"},"listState":{"list":{},"objectTitle":"","status":"initial","pageType":null,"objectId":null,"page":1,"sortField":"time","sortOrder":1,"categoriesIds":[],"articleTypes":[],"filterData":{},"filterDataLoadedStatus":"initial","pageSize":10},"adsState":{"pageScripts":{"headers":{"timestamp":"2024-11-22T05:50:01+00:00"},"adsId":0,"data":{"scripts":[{"pages":["all"],"location":"header","script":"\r\n<script src=\"https://cdn.optimizely.com/js/10563184655.js\"></script>","enabled":false},{"pages":["all"],"location":"header","script":"\r\n<script>var _comscore = _comscore || [];_comscore.push({ c1: \"2\", c2: \"15097263\" });(function() {var s = document.createElement(\"script\"), el = document.getElementsByTagName(\"script\")[0]; s.async = true;s.src = (document.location.protocol == \"https:\" ? \"https://sb\" : \"http://b\") + \".scorecardresearch.com/beacon.js\";el.parentNode.insertBefore(s, el);})();</script><noscript><img src=\"https://sb.scorecardresearch.com/p?c1=2&c2=15097263&cv=2.0&cj=1\" /></noscript>\r\n","enabled":true},{"pages":["all"],"location":"footer","script":"\r\n<script type='text/javascript'>\r\n(function(){var g=function(e,h,f,g){\r\nthis.get=function(a){for(var a=a+\"=\",c=document.cookie.split(\";\"),b=0,e=c.length;b<e;b++){for(var d=c[b];\" \"==d.charAt(0);)d=d.substring(1,d.length);if(0==d.indexOf(a))return d.substring(a.length,d.length)}return null};\r\nthis.set=function(a,c){var b=\"\",b=new Date;b.setTime(b.getTime()+6048E5);b=\"; expires=\"+b.toGMTString();document.cookie=a+\"=\"+c+b+\"; path=/; \"};\r\nthis.check=function(){var a=this.get(f);if(a)a=a.split(\":\");else if(100!=e)\"v\"==h&&(e=Math.random()>=e/100?0:100),a=[h,e,0],this.set(f,a.join(\":\"));else return!0;var c=a[1];if(100==c)return!0;switch(a[0]){case \"v\":return!1;case \"r\":return c=a[2]%Math.floor(100/c),a[2]++,this.set(f,a.join(\":\")),!c}return!0};\r\nthis.go=function(){if(this.check()){var a=document.createElement(\"script\");a.type=\"text/javascript\";a.src=g;document.body&&document.body.appendChild(a)}};\r\nthis.start=function(){var t=this;\"complete\"!==document.readyState?window.addEventListener?window.addEventListener(\"load\",function(){t.go()},!1):window.attachEvent&&window.attachEvent(\"onload\",function(){t.go()}):t.go()};};\r\ntry{(new g(100,\"r\",\"QSI_S_ZN_5o5yqpvMVjgDOuN\",\"https://zn5o5yqpvmvjgdoun-wiley.siteintercept.qualtrics.com/SIE/?Q_ZID=ZN_5o5yqpvMVjgDOuN\")).start()}catch(i){}})();\r\n</script><div id='ZN_5o5yqpvMVjgDOuN'></div>\r\n","enabled":false},{"pages":["all"],"location":"header","script":"\r\n<script>\r\n (function(h,o,t,j,a,r){\r\n h.hj=h.hj||function(){(h.hj.q=h.hj.q||[]).push(arguments)};\r\n h._hjSettings={hjid:257151,hjsv:6};\r\n a=o.getElementsByTagName('head')[0];\r\n r=o.createElement('script');r.async=1;\r\n r.src=t+h._hjSettings.hjid+j+h._hjSettings.hjsv;\r\n a.appendChild(r);\r\n })(window,document,'https://static.hotjar.com/c/hotjar-','.js?sv=');\r\n</script>","enabled":false},{"pages":["article"],"location":"header","script":" <script src=\"//get.s-onetag.com/bffe21a1-6bb8-4928-9449-7beadb468dae/tag.min.js\" async defer></script>","enabled":true},{"pages":["homepage"],"location":"header","script":"<meta name=\"facebook-domain-verification\" content=\"irk8y0irxf718trg3uwwuexg6xpva0\" />","enabled":true},{"pages":["homepage","article","category","search"],"location":"footer","script":"\r\n<noscript>\r\n<img height=\"1\" width=\"1\" src=\"https://www.facebook.com/tr?id=256338321977984&ev=PageView&noscript=1\"/>\r\n</noscript>\r\n","enabled":true}]}},"pageScriptsLoadedStatus":"success"},"navigationState":{"navigationCollections":[{"collectionId":287568,"title":"BYOB (Be Your Own Boss)","hasSubCategories":false,"url":"/collection/for-the-entry-level-entrepreneur-287568"},{"collectionId":293237,"title":"Be a Rad Dad","hasSubCategories":false,"url":"/collection/be-the-best-dad-293237"},{"collectionId":295890,"title":"Career Shifting","hasSubCategories":false,"url":"/collection/career-shifting-295890"},{"collectionId":294090,"title":"Contemplating the Cosmos","hasSubCategories":false,"url":"/collection/theres-something-about-space-294090"},{"collectionId":287563,"title":"For Those Seeking Peace of Mind","hasSubCategories":false,"url":"/collection/for-those-seeking-peace-of-mind-287563"},{"collectionId":287570,"title":"For the Aspiring Aficionado","hasSubCategories":false,"url":"/collection/for-the-bougielicious-287570"},{"collectionId":291903,"title":"For the Budding Cannabis Enthusiast","hasSubCategories":false,"url":"/collection/for-the-budding-cannabis-enthusiast-291903"},{"collectionId":299891,"title":"For the College Bound","hasSubCategories":false,"url":"/collection/for-the-college-bound-299891"},{"collectionId":291934,"title":"For the Exam-Season Crammer","hasSubCategories":false,"url":"/collection/for-the-exam-season-crammer-291934"},{"collectionId":301547,"title":"For the Game Day Prepper","hasSubCategories":false,"url":"/collection/big-game-day-prep-made-easy-301547"}],"navigationCollectionsLoadedStatus":"success","navigationCategories":{"books":{"0":{"data":[{"categoryId":33512,"title":"Technology","hasSubCategories":true,"url":"/category/books/technology-33512"},{"categoryId":33662,"title":"Academics & The Arts","hasSubCategories":true,"url":"/category/books/academics-the-arts-33662"},{"categoryId":33809,"title":"Home, Auto, & Hobbies","hasSubCategories":true,"url":"/category/books/home-auto-hobbies-33809"},{"categoryId":34038,"title":"Body, Mind, & Spirit","hasSubCategories":true,"url":"/category/books/body-mind-spirit-34038"},{"categoryId":34224,"title":"Business, Careers, & Money","hasSubCategories":true,"url":"/category/books/business-careers-money-34224"}],"breadcrumbs":[],"categoryTitle":"Level 0 Category","mainCategoryUrl":"/category/books/level-0-category-0"}},"articles":{"0":{"data":[{"categoryId":33512,"title":"Technology","hasSubCategories":true,"url":"/category/articles/technology-33512"},{"categoryId":33662,"title":"Academics & The Arts","hasSubCategories":true,"url":"/category/articles/academics-the-arts-33662"},{"categoryId":33809,"title":"Home, Auto, & Hobbies","hasSubCategories":true,"url":"/category/articles/home-auto-hobbies-33809"},{"categoryId":34038,"title":"Body, Mind, & Spirit","hasSubCategories":true,"url":"/category/articles/body-mind-spirit-34038"},{"categoryId":34224,"title":"Business, Careers, & Money","hasSubCategories":true,"url":"/category/articles/business-careers-money-34224"}],"breadcrumbs":[],"categoryTitle":"Level 0 Category","mainCategoryUrl":"/category/articles/level-0-category-0"}}},"navigationCategoriesLoadedStatus":"success"},"searchState":{"searchList":[],"searchStatus":"initial","relatedArticlesList":[],"relatedArticlesStatus":"initial"},"routeState":{"name":"Article3","path":"/article/academics-the-arts/math/basic-math/how-to-measure-triangles-149990/","hash":"","query":{},"params":{"category1":"academics-the-arts","category2":"math","category3":"basic-math","article":"how-to-measure-triangles-149990"},"fullPath":"/article/academics-the-arts/math/basic-math/how-to-measure-triangles-149990/","meta":{"routeType":"article","breadcrumbInfo":{"suffix":"Articles","baseRoute":"/category/articles"},"prerenderWithAsyncData":true},"from":{"name":null,"path":"/","hash":"","query":{},"params":{},"fullPath":"/","meta":{}}},"dropsState":{"submitEmailResponse":false,"status":"initial"},"profileState":{"auth":{},"userOptions":{},"status":"success"}}

How to Measure Triangles

By: Mark Zegarelli and

Updated: 04-25-2016

From The Book: Basic Math & Pre-Algebra For Dummies

Basic Math & Pre-Algebra For Dummies

$Book image$

Explore Book Buy On Amazon

You can measure the perimeter and area of all triangles. There also is a special feature of right triangles that allows you to measure them more easily.

Finding the perimeter and area of a triangle

Mathematicians have no special formula for finding the perimeter of a triangle — they just add up the lengths of the sides.

To find the area of a triangle, you need to know the length of one side — the base (b for short) — and the height (h). Note that the height forms a right angle with the base. This figure shows a triangle with a base of 5 cm and a height of 2 cm:

Here's the formula for the area of a triangle:

So here's how to figure out the area of a triangle with a base of 5 cm and a height of 2 cm:

Finding the third side of a right triangle

The long side of a right triangle (c) is called the hypotenuse, and the two short sides (a and b) are called the legs:

The most important right triangle formula is the Pythagorean theorem:

This formula allows you to find the hypotenuse of a triangle, given only the lengths of the legs. For example, suppose the legs of a triangle are 3 and 4 units. Here's how to use the Pythagorean theorem to find the length of the hypotenuse:

So when you multiply c by itself, the result is 25. Therefore, take the square root of both sides to find:

c = 5

The length of the hypotenuse is 5 units.

About This Article

This article is from the book:

Basic Math & Pre-Algebra For Dummies ,

About the book author:

Mark Zegarelli is a professional writer with degrees in both English and Math from Rutgers University. He has earned his living for many years writing vast quantities of logic puzzles, a hefty chunk of software documentation, and the occasional book or film review. Along the way, he’s also paid a few bills doing housecleaning, decorative painting, and (for ten hours) retail sales. He likes writing best, though.

This article can be found in the category:

Basic Math ,