Question

Given F(x) =3x^2 - 4 and F(a) = 8 find a

Answer 1

$F(x)=3x^2-4\\\\F(a)=8\to3a^2-4=8\qquad\text{add 4 to both sides}\\\\3a^2=12\qquad\text{divide both sides by 3}\\\\a^2=4\to a=\pm\sqrt4\to a=\pm2\\\\Answer:\ \boxed{A.\ \pm2}$