Evaluate 4xdx\displaystyle \int{4}^{{x}}{\left.{d}{x}\right.}.
First rewrite 4x=e?\displaystyle {4}^{{x}}={e}^{?}  
Next make the substitution u =  
Now integrate with respect to u to get   + C
So 4xdx\displaystyle \int{4}^{{x}}{\left.{d}{x}\right.} =   + C