Baluncore, I think the reason I was having trouble is because the answer they provided was missing the plus sign, a previous professor of mine provided me a pdf file explaining how they get Rin and it definitely shows that it should be Rin = RB || ( rpi + RE(beta +1)).
[Mentor's Note: Thread Moved from EE Forum]
This link has the picture, for some reason it wasnt showing in this post. http://i.imgur.com/TYlb32t.jpg
Here is my problem, I am supposed to use this circuit and solve for Av and Rin. My problem is that I have solved for Av but I can't solve for Rin...