I'm struggling to see how when you differentiate 3(4-t)^-1 that you get 3(4-t)^-2 Surely this should be -3(4-t)^-2 ??? Regards Richard
No, it is 3(4-t)^-2 as the -ve from the -1 and the -ve from the -t combine to give a +ve outside the bracket.
