First derive the #()^2# as it is then multiply by the derivative of the #ln# (red) and finally multply by the derivative of the argument of the #ln# (blue): #f'(x)=2(ln(6x+8))^(2-1)*color(red)(1/(6x+8))*color(blue)(6)=# #=12/(6x+8)ln(6x+8)=12/(2(3x+4))ln(6x+8)=# #=6/(3x+4)ln(6x+8)#