Q. 44.3( 3 Votes )

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

Answer :

Given: the radius of a circle is increasing at the rate of 0.7 cm/sec.


To find rate of increase of its circumference


Let the radius of the given circle be r cm at any instant time.


Then according to the given criteria,


Rate of radius of a circle is increasing is,


Then the circumference of the circle at any time t will be


C = 2r cm.


Applying derivative with respect to time on both sides we get,




[from equation(i)]


Hence the rate of increase of the circle’s circumference will be 1.4 cm/sec


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