Question

$\text{If}f\left(x\right)=x^2-1,\text{then find}fof.$

• A. $x^8+4x^4-4x^6-1$
• B. $x^4-2x^2$
• C. $x^4-2x^2-1$
• D. $x^4-2x^2-2$

Answer 1

The correct option is B $x^4-2x^2$

$\text{Given}f\left(x\right)=x^2-1$
$fof=f\left\{f\right(x\left)\right\}$
$=f\{x^2-1\}=\left\{\right(x^2-1{)}^2-1\}=\{x^4+1-2x^2-1\}=\{x^4-2x^2\}$