Answer
$\csc \theta$
Work Step by Step
Here, we have $\sin \theta(1+\cot^2 \theta)$
Re-arrange the given equation as: $=\sin \theta (\csc^2 \theta)$
$=\sin \theta \times \csc \theta \times \csc \theta$
$=\dfrac{\sin \theta}{\sin \theta} \times \csc \theta$
$=\csc \theta$