Have a new tutor who has failed to teach us most of his assignment, I've finally got stuck on derivation of the formula G=E/2(1+v).

any help would be much appreciated!

http://www.nptel.ac.in/courses/Webcourse-contents/IIT-ROORKEE/strength%20of%20materials/lects%20&%20picts/image/lect10/lecture10.htm