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## Homework Statement

Find the derivative of arctan(6x).

## Homework Equations

## The Attempt at a Solution

Ok, I know the derivative of arctan(x) is 1/(x^2 + 1).

So I am trying to make the substitution u = 6x.

Then the derivative of arctan(u) should be 1/(u^2 + 1)... and therefore 1/(36x^2 +1).

But that's not right... what am I doing wrong?