Question

If the function is $f:R\to R,g:R\to R$ are defined as $f\left(x\right)=2x+3,g\left(x\right)=x^2+7$ and $f\left[g\right(x\left)\right]=25$ then $x=$

• A. $f\left(x\right)$
• B. $\pm 2$
• C. $\pm 3$
• D. $\pm 4$

Answer 1

Answer: (B)

$\pm 2$

$f\left(g\right(x\left)\right)=f(x^2+7)=25$
$=2(x^2+7)+3$
$=2x^2+17$
$\Rightarrow 2x^2=8$
$x^2=4\Rightarrow x=\pm 2$