If the pth term of an AP is q and the qth term is p, then its (p+q)th term is:

Question

G1 Physics · Accepted Answer

a+(p−1)d=q and a+(q−1)d=p. Subtracting gives (p−q)d=q−p, so d=−1 (for p≠q). Then a=p+q−1, and Tₚ₊q=a+(p+q−1)d=0.