Answers

2014-06-21T19:48:29+05:30
The area of a circle is 

A = 
 \pi *r^2 

Take the derivative with respect to time 

dA/dt = 2*
 \pi *r*dr/dt 

Substitute the appropriate values 

dA/dt = 2*
 \pi *2*3 = 12  \pi  cm^{2} /sec
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2014-06-22T11:54:17+05:30
Circumference of circle 
C = 2*pi*r
dC/dt = 2*pi*dr/dt = k
area of circle
A = 2*pi*r²
dA/dt = 2*pi*2rdr/dt
dA/dt = 2*3*k = 6k
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