Source TeX:

\begin{array}{lcl}\sin(\theta)\neq 0&\Leftrightarrow& \theta\neq -\pi, 0,\pi, 2\pi,\dots\neq k\pi\\\sin(3x)\neq 0&\Leftrightarrow&3x\neq k\pi\\&\Leftrightarrow& x\neq\dfrac{k\pi}{3}\end{array}