5.25: I'm a little confused-- I used the law of cosines on angle B and got 2 equations. dividing out cosB, I found \( \frac{33^2+m^2-21^2}{(33-n)^2+(m-n)^2+n^2}=\frac{33m}{(33-n)(m-n)} \), which is really complicated. When I tried using the law of cosines on A, I found 21^2+33^2-m^2=2x21x33xcosA, which doesn't seem to form any relationships between n and m.

5.26: an+2−an+1=(n+2)(an+1-an) I'm not quite sure what to do/ how to solve this equation though. BTW, where will these equations be covered in math comp learning? I seem to be really bad at solving equations like these. 

5.27: I still didn't quite understand. If I know the roots are 1, -1, 2, -2, wouldn't I know that {a,b,c,d}={1,2,3,4}? Then abcd would be determined. Regarding adding the roots together, we would get abc+abd+acd+bcd=0, using Veita's Theorom. However I'm not quite sure what to do next.

5.28: I think I understand the question now. Could you please give me another hint?

5.29:  Since p is a factor of 2n-1, and is also a factor of either n-2 or n+1, then p must be factors of both n-2 and n+1 , which means p<=3. Since 2n-1 is odd, p isn't 1, leaving us with 3 and 1. 2n-1=3, n=2