Is a rule that describes how the side length's of right angle triangles are related.
It is often written as a2 + b2 = c2 where a and b are the two shorter sides of a right angle triangle and c is the longest side and called the hypotenuse.
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What this means is that the area of square a added to the area of square b is the same as the area of square c.
This is possibly easier to understand with an example;
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