Explain briefly how the sign of indicates whether a parametric curve is concave…

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

Problem

Explain briefly how the sign of

\dfrac{d^{2}y}{dx^{2}}

indicates whether a parametric curve is concave upward or concave downward at a point.