Phythagoras' Theorem states that in any right-angled triangle, the area of the square whose side is the hypotenuse (the side opposite the right angle) is equal to the sum of the areas of the squares whose sides are the two legs (the two sides that meet at a right angle).

This is usually summarized as The square on the hypotenuse is equal to the sum of the squares on the other two sides.'

If we let c be the length of the hypotenuse and a and b be the lengths of the other two sides, the theorem can be expressed as the equation


or, solved for c


Example[edit | edit source]

First substitute the numbers in


c = 5

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