The sum of first 3terms of an increasing gp is 21 and the sum of their squares is 189.the sum of its n terms is
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Let the three numbers in G.P. be a, ar and ar2.
a + ar + ar2 = 21 (Given)
⇒ a2( 1+ r + r2)2 = 441 ... (1)
(a)2 + (ar)2 + (ar2)2 = 189 (Given)
⇒ a2 (1 + r2 + r4) = 189 ... (2)
From (1) and (2), we get
Thus, the three numbers in G.P. are 3, 6 and 12.
a + ar + ar2 = 21 (Given)
⇒ a2( 1+ r + r2)2 = 441 ... (1)
(a)2 + (ar)2 + (ar2)2 = 189 (Given)
⇒ a2 (1 + r2 + r4) = 189 ... (2)
From (1) and (2), we get
Thus, the three numbers in G.P. are 3, 6 and 12.
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