InterviewSolution
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If a, b, c are in G.P., prove that the following are also in G.P.:(i) a2, b2, c2(ii) a3, b3, c3(iii) a2 + b2, ab + bc, b2 + c2 |
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Answer» (i) a2, b2, c2 Given that a, b, c are in GP. By using the property of geometric mean, b2 = ac on squaring both the sides we get, (b2)2 = (ac)2 (b2)2 = a2c2 ∴ a2, b2, c2 are in G.P. (ii) a3, b3, c3 Given that a, b, c are in GP. By using the property of geometric mean, b2 = ac on squaring both the sides we get, (b2)3 = (ac)3 (b2)3 = a3c3 (b3)2 = a3c3 ∴ a3, b3, c3 are in G.P. (iii) a2 + b2, ab + bc, b2 + c2 Given that a, b, c are in GP. By using the property of geometric mean, b2 = ac a2 + b2, ab + bc, b2 + c2 or (ab + bc)2 = (a2 + b2) (b2 + c2) [by using the property of GM] Let us consider LHS: (ab + bc)2 Upon expansion we get, (ab + bc)2 = a2b2 + 2ab2c + b2c2 = a2b2 + 2b2(b2) + b2c2 [Since, ac = b2] = a2b2 + 2b4 + b2c2 = a2b2 + b4 + a2c2 + b2c2 {again using b2 = ac } = b2(b2 + a2) + c2(a2 + b2) = (a2 + b2)(b2 + c2) = RHS ∴ LHS = RHS Hence a2 + b2, ab + bc, b2 + c2 are in GP. |
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