(x-8)^2
x^2-16x+64
(2x-4)(2x+4)
4x^2-16
(3x-5)^2
9x^2-30x+25
(2r+7s)^2
4r^2+28rs+49s^2
(-5x-4y)^2
25x^2+40xy+16y^2