A particle moves according to for

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

Problem

A particle moves according to

\mathbf r(t)=\langle \cos t,\, \sin t\rangle

for

0< t<2\pi

. How many times in this interval does the particle reverse direction in its

x

–coordinate? (a) 4 (b) 1 (c) 0 (d) 2