InterviewSolution
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InterviewSolution
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The sum of first three terms of a G.P. is 21/2 and their product is 27. Find the common ratio.(a) 2(b) 1/2(c) 2 or 1/2(d) neither 2 nor 1/2This question was addressed to me in unit test.Enquiry is from Geometric Progression(G.P.) topic in section Sequences and Series of Mathematics – Class 11 |
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Answer» RIGHT option is (c) 2 or 1/2 Explanation: LET three terms be a/R, a, a*r. Product = 27 => (a/r) (a) (a*r) = 27 => a^3 = 27 =>a = 3. Sum = 21/2 => (a / r + a + a*r) = 21/2 => a (1 / r + 1 + 1*r) = 21/2 => (1 / r + 1 + 1*r) = (21/2)/3 = 7/2 => (r^2 + r + 1) = (7/2) r => r^2 – (5/2) r + 1 = 0 => r = 2 and 1/2. |
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