Answer
No real solution
Work Step by Step
Squaring both sides, the given expression is equivalent to
$$
f=3f+6
.$$
Using properties of equality, the equation above is equivalent to
$$\begin{aligned}
-2f&=6
\\
f&=-3
.\end{aligned}$$
Checking:
$$\begin{aligned}
\sqrt{-3}\overset{?}=\sqrt{3(-3)+6}
.\end{aligned}$$Since $\sqrt{-3}$ is not a real number, it means the given equation has no real solution.
