Evaluate 8xdx\displaystyle \int{8}^{{x}}{\left.{d}{x}\right.}.
First rewrite 8x=e?\displaystyle {8}^{{x}}={e}^{?}  
Next make the substitution u =  
Now integrate with respect to u to get   + C
So 8xdx\displaystyle \int{8}^{{x}}{\left.{d}{x}\right.} =   + C