In a right triangle, the hypotenuse is always the longest side. Plus, the hypotenuse squared has to equal the sum of the squares of the other 2 sides. For the first "triangle" above: does
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? Let's check. 196 = 25 + 16 so does 196 = 41? Obviously not. So that is not a right triangle. Let's check the second one the same way. Does
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? 25 = 9 + 16. Does 25 = 25? Of course it does! So 1 is not a right triangle, but 2 is!