Question 133018
Sorry I do not have your textbook so can't use that as an example. However, generally, I prefer to do proof as follows:

1) ALWAYS restate the problem. 
2) Then beginning with the supposition, work your way toward "what is to be proven".
3) At each small step along the way, you MUST state which mathematical principle allows you to make that step. Usually that is something basic, like commutative property, associative property, identity, etc

Sometimes it is not clear how to go from start to finish. Sometimes you end up working from both ends toward the middle. Then once you get a thread of simple steps that works from end to end, rewrite the solution from start to end.

Sorry I can be more helpful. Perhpas you can post the problem you wish to 'prove"