Basic Math & Pre-Algebra All-in-One For Dummies (+ Chapter Quizzes Online)
The trick is to split up the shape into smaller rectangles for which you either know or can figure out the length of each side. This is a little bit more of an art than a science – but as with everything else in maths and life, the more you practise, the easier the method gets.
Take the following steps if you need to find the area of a shape that isn’t a rectangle but is full of right angles:
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Try to find somewhere to draw a line that splits the shape into two, smaller rectangles.
If not, draw a line that splits off one rectangle and try to split the rest of the shape up into smaller rectangles. How many rectangles you have doesn’t matter – but you’re less likely to make mistakes if you use as few shapes as possible.
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Work out the sides of each rectangle you have left over.
You may need to do a bit of lateral thinking, but normally you just need to take something away from the total length of a side.
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Find the area of each rectangle by multiplying the sides together.
Write the answer in the middle of the rectangle so you don’t forget it.
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Add up all of the areas you just worked out.
The answer is your total area.
On the right, the rectangle is split up in a different way, giving three separate shapes. Again, work out the lengths of the sides, find the areas and add the areas to get a final answer. You end up with the same answer using both methods.