Question

I know the answer I just need to know how to solve it. The highlighted is the answer.

Answer 1

$x^2+4x+4 = 8\\\\\implies x^2+2\cdot 2 \cdot x+2^2 = 8\\ \\\implies (x+2)^2 = 8\\\\\implies x+2 =\pm\sqrt 8\\\\\implies x +2 = \pm\sqrt{4 \times 2}\\\\\implies x +2 = \pm2\sqrt 2\\\\\implies x =-2 \pm2\sqrt2$