State the required conditions on and for the tangent to the parametric curve to be

MATHEMATICS · Subjective · AP · Calculus BC · Parametric, Polar, and Vector-Valued Functions · Parametric, Polar, and Vector-Valued Functions

Problem

State the required conditions on

\dfrac{dx}{dt}

and

\dfrac{dy}{dt}

for the tangent to the parametric curve

x=f(t),\;y=g(t)

to be (a) horizontal, and (b) vertical.