If the area of a circle is

MATHEMATICS · Single correct · AP · Calculus AB · Contextual Applications of Differentiation · Contextual Applications of Differentiation

Problem

A=\pi r^{2}

, which of the following correctly gives

\dfrac{dA}{dt}

in terms of

r

and

\dfrac{dr}{dt}

? (a)

\pi r\,\dfrac{dr}{dt}

(b)

2\pi r\,\dfrac{dr}{dt}

(c)

4\pi r\,\dfrac{dr}{dt}

(d)

3\pi r\,\dfrac{dr}{dt}