The radius of a circle is increasing at the rate of `0.7 cm//s`. What is the rate of increase of its circumference ?

Explanation

Let r be the radius of the circle and t be the time
Then, circumference of the circle, `C=2pir`….(i)
`A//Q, (dr)/dt=0.7`
Now, differentiating(i)w.r.t. time t, we get
`implies (dC)/dt=2pi(0.7)=2xx22/7xx0.7=4.4`
`therefore` Rate of increase of circumference of the circle=`4.4 cm//s`.