What is the length of the hypotenuse if a triangles legs are 9 and 8?

9 squared is 81. 8 squared is 64.

81 + 64 = 145

sqrt(145)

It's in between 12 and 13.

closer to 12 since 12 squared is 144 and 145 is only 1 away.

NOTE: Only works if it is a right triangle.