Answer
Counterexample: $\theta=\pi$
(sample answer)
Work Step by Step
The LHS is a POSITIVE square root...
so we look for a $\theta$ that produces a negative RHS.
For example, if $\theta=\pi,$
$RHS=0+(-1)=-1$
LHS is positive, RHS is negative.
They can't be equal, so the identity is not valid.