# Question d6521

Apr 22, 2017

${x}^{4} + 10 {x}^{2} + 30$

#### Explanation:

I am using this approach to show what is going on.

Let $\textcolor{g r e e n}{g \left(x\right) = a = {x}^{2} + 5}$

so " "color(brown)(g(color(white)(.)color(green)(g(x)color(white)(.)))->g(color(green)(a))=(color(green)(a)^2+5)#

Substitute for $a$ giving

${a}^{2} + 5 \text{ "->" } {\left({x}^{2} + 5\right)}^{2} + 5$

$\text{ } {x}^{4} + 10 {x}^{2} + 25 + 5$

$\text{ } {x}^{4} + 10 {x}^{2} + 30$