What is the derivative of #2*pi*r #?

1 Answer
Alan P.
Dec 9, 2016

#(d(2pir))/(dr)#
#color(white)("XXX")=2pi(dr)/(dr)# by the Constant Rule for Derivatives

#color(white)("XXX")=2pi#

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The Constant Rule for Derivatives tells us that
If #f(x)=c * g(x)# for some constant #c#
then #f'(x)=c * g'(x)#

In this case #f(r)=2pir; c=2pi, and g(r)=r#

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