This is a question for those of you interested in mathematics or are taking proof classes: when will you know when you are writing too much or too little in a proof? I'm taking a proof class right now, and my professor doesn't do a good job of explaining this to me and just shows/implies the right answer.

I don't think there's a set limit either way. As long as you make sure to discuss all the relevant key ideas and theorems, then you have formed a sufficient proof. Try to be as direct as possible and it doesn't hurt to take shortcuts now and then. Remember to always clearly state what the goal of the proof is, and set up the boundaries needed (eg: x is a nonzero real number). Also, make sure you connect the "given" to the thing to be proved. I've noticed a lot of students forget to do this.

If possible, try to explain the concept to someone outside the class so you can try to get a better handle on the proof. At the same time, you don't want to spend too much time going over the very fine details. Again it's all about balance in my mind.

e) none of the above because the measure of angle cba is 101°