I have a problem that seems really basic, but for whatever reason I keep messing up... f(r) = 7/(1+r)^2 Find the average value of the function on the interval [1,5] I let u = 1+r so   du = dx and integral 7u^-2 du integrated I get -7u^(-1)  and the new interval is [2,6] -7(6)^-1+7(2)^-1 = 7/3 So the answer I keep coming up with is 7/3 which is wrong evidently........ Can anyone help?