Problem
x^2 - 8x + 16
Solution
For this case we need to find two numbers a and b that added would be -8 and multiplied 16 and then we see that the two numbers are:
a= b= -4
because a+b = -4-4=-8
a*b= -4 (-4) = 16
And then the best answer for this case is:
(x-4)²