Question

If the functions $f : R \rightarrow R , g : R \rightarrow R$ are defined as $f(x) = 2x +3, g(x) = x^2 + 7$ and $f[g(x)] = 25$ then $x =$

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

Answer 1

Answer: (B)

$\pm 2$

Answer 2

$f(g(x)) = 25\: \Rightarrow \: 2g(x) + 3 = 25$ $\Rightarrow \, g(x) = 11 \Rightarrow x^2 + 7 = 11 \Rightarrow x = \pm 2$