NCERT Class XI Mathematics - Sequences and Series - Solutions

Question : 36

Total: 106

The 5th, 8th and 11th terms of a G.P. are p, q and s, respectively. Show that q2 = ps.

Solution:

We are given
a5 = ar4 = p .... (i)
a8 = ar7 = q .... (ii)
a11 = ar10 = s .... (iii)
Now multiply (i) and (iii), we get
ps = a2r14 = (ar7)2 = q2 [using (ii)]
⇒ q2 = ps.

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