Answer
{$\dfrac{-1}{3},\dfrac{-3}{2}$}
Work Step by Step
Plug $f(x)=2$
Therefore, we have $3(\dfrac{1}{x}+1)^2+5(\dfrac{1}{x}+1)=2$
This implies $[3(\dfrac{1}{x}+1)-1][(\dfrac{1}{x}+1)+2]=0$
Now, $3(\dfrac{1}{x}+1)-1=0$
or, $-2x=3$
or, $x=\dfrac{-3}{2}$
and $(\dfrac{1}{x}+1)+2=0$
or, $-3x=1$
or, $x=\dfrac{-1}{3}$
Solution set: $x=${$\dfrac{-1}{3},\dfrac{-3}{2}$}