Answer: A
(He has the side lengths in the wrong place in the cosine ratio)
1 1/6, 1 2/3, 1 5/6 is the order. :) hope I helped!
If you're just integrating a vector-valued function, you just integrate each component:


The first integral is trivial since
.
The second can be done by substituting
:

The third can be found by integrating by parts:


