If the 2nd,5th and 9th terms of non-constant A.P. are in G.P., then the common ratio of this G.P. is:
a+d,a+4d,a+8d are in G.P.(a+4d)2=(a+d)(a+8d)⇒a2+8ad+16d2=a2+9ad+8d2⇒8d2=ad⇒ad=8∴Common ratio=a+4da+d=8+48+1=43
If pth, qth and rth terms of an A.P. are in G.P., then the common ratio of this G.P. is