Answer: 12
If you are trying to find the length of the long side of the triangle, use this formula: a^2 + b^2 = c^2
So, for you, it'd be 3^2 + 4^2 = 12^2
If it isn't, use this formula: a^2 - b^2 = c^2
EX: 3^2 - 12^2 = 4^2
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