Question

[Related Rates]

If A is the area of a circle with radius r and the circle expands as time passes, find dA/dt in terms of dr/dt

Answer 1

like the last one
\[A=\pi r^2\]
\[\frac{dA}{dt}=\frac{dA}{dr}\frac{dr}{dt}=2\pi r\frac{dr}{dt}\]