Derivative of f(a) = 2pirsquared

[rafirank]

If the area of a circle is a = πr² then should not the derivative be 2πr? I have a textbook that reads the derivative is 2π which seems to me to be an error?

 

[Deleted member 4993]

If the area of a circle is a = πr² then should not the derivative be 2πr? I have a textbook that reads the derivative is 2π which seems to me to be an error?

You are correct.

However, it may have been implied in the problem that they are looking at a special case of r = 1.

Check the title of your thread and make sure it is correct