In an AP, Sp=qS_p = qSp=q and Sq=pS_q = pSq=p (with p≠qp \neq qp=q). Find Sp+qS_{p+q}Sp+q.
−(p+q)-(p+q)−(p+q)
p+qp+qp+q
000
p−qp-qp−q