Question

If $f\left(x+\frac{1}{x}\right)=x^3+\frac{1}{x^3}-7\left(x+\frac{1}{x}\right)$, then the value of (fof) (3) equals

• A. -3
• B. 3
• C. 10
• D. 5

Answer 1

Answer: (B)

Let $x+\frac{1}{x}=t$
$f(t)=t^3-10t$
$f(3)=27-30=-3$
$(f\circ f)(3)=f(f(3))=f(-3)=-27+30=3$