Ok so I am a bit confused by the shell method. My prof has given us a general forumula for using the shell method which I understand $\displaystyle V=\int^b_a 2\pi (x-M)[u(x)-l(x)]dx$

where $\displaystyle M$ is the line which to rotate around, $\displaystyle u(x)$ is the upper curve, and $\displaystyle l(x)$ is the lower curve.

When presented with the following question where we have to rotate about $\displaystyle x=5$ as shown on the following graph when I simply substituted 5 in for M, giving me $\displaystyle (x-5)$ for the first part I get the wrong answer but $\displaystyle (5-x)$ gives me the correct the answer.

Looking at some of the examples I have it would appear that if the axis of rotation is to the right of our functions it reverses the order of $\displaystyle (x-M)$ to $\displaystyle (M-x)$. Is this correct to assume?