In an arithmetic progression, the pth term is q and the qth term is p, where p=q.
a. (a) Form two equations in the first term a and the common difference d using the given information, and hence obtain the value of d.
b. (b) Using the value of d, find the first term a in terms of p and q.
c. (c) Show that the (p+q)th term of the progression is 0.