Respuesta :

LammettHash
The area of a circle in terms of the circle's radius [tex]r[/tex] is

[tex]A=\pi r^2[/tex]

Differentiating both sides with respect to [tex]t[/tex], you get

[tex]\dfrac{\mathrm dA}{\mathrm dt}=2\pi r\dfrac{\mathrm dr}{\mathrm dt}[/tex]