=x^2+16x+64+2(x^2+6x-16)+x^2-4x+4
=2x^2+12x+68+2x^2+12x-32
=4x^2+24x+36
\(\left(x+8\right)\left(x+8\right)-2\left(x+8\right)\left(x-2\right)+\left(x-2\right)^2\)
\(=\left(x+8\right)^2-2\left(x+8\right)\left(x-2\right)+\left(x-2\right)^2\)
\(=\left[\left(x+8\right)-\left(x-2\right)\right]^2\)
\(=\left(x+8-x+2\right)^2\)
\(=10^2\)
\(=100\)