### Chain Rule & Integration by Substitution

Fluency exercise

A curve in the $x-y$ plane is defined parametrically in terms of a parameter $t$ as $x=2 \cos t,\quad y=3 \sin t.$
Find an expression for $\dfrac{dy}{dx}$ in terms of $t$.
Are there any values of $t$ for which $\dfrac{dy}{dx}$ is undefined? What would that mean?