Remember that if a side is across from the 90 degree angle in a triangle, it’s the hypotenuse.
In a 90 degree triangle, the two smaller sides to the power of 2 equals to the hypotenuse to the power of 2
The equation: 25^2+x^2=65^2
Simplify: 625+x^2=4225
4225-625=x^2
x^2=3600
x=root3600
x=plusminus60