Question

Let f be a function defined by $f\left(x\right)=5x^2+2,x\in R$. Find a such that $f\left(a\right)=22$

Answer 1

$f\left(x\right)=5x^2+2$

$f\left(a\right)=22$

$\Rightarrow 5a^2+2=22$

$5a^2=22-2=20$

$a^2=4$

$a=\pm \sqrt{4}$

$a=\pm 2$