281

a)
\left(x+2\right)^2=\left(x-4\right)\left(x+4\right)
x^2+2\cdot x\cdot2+2^2=x^2-4^2
x^2+4x+4=x^2-16
x^2-x^2+4x=-16-4
4x=-20
x=-5
b)