to be a perfect square C needs to be a number that can be squared
and the middle term needs to be able to be multiplied by 2 or -2 of the square of the 3rd term (C)
so in this case C = 25
25 can be squared ( square root of 25 is 5)
square root of 25 (5) times 2 = 10 ( 2nd term)
C = 25
