expand (x-4)^2
Let's write in expanded form: (x -4)2
(x -4)·(x -4)
x·x + x·-4 -4x -4·-4
x·x = x2x·-4 = -x·4-4·-4 = 16
x2 -x·4 -4x + 16
Result:   x2 -8x + 16