InterviewSolution
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The sum of three numbers a, b, c in A.P. is 18. If a and b are each increased by 4 and c is increased by 36, the new numbers form a G.P. Find a, b, c. |
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Answer» Let the first term of an A.P. be ‘a’ and its common difference be‘d’. b = a + d; c = a + 2d. Given: a + b + c = 18 3a + 3d = 18 or a + d = 6. d = 6 – a … (i) Now, according to the question: a + 4, a + d + 4, and a + 2d + 36 they are now in GP, that is: (a + d + 4)/(a + 4) = (a + 2d + 36)/(a + d + 4) a2 + d2 + 16 + 8a + 2ad + 8d = a2 + 4a + 2da + 36a + 144 + 8d d2 – 32a – 128 (6 – a)2 – 32a – 128 = 0 36 + a2 – 12a – 32a – 128 = 0 a2 – 44a – 92 = 0 a2 – 46a + 2a – 92 = 0 a(a – 46) + 2(a – 46) = 0 a = – 2 or a = 46 d = 6 –a d = 6 – (– 2) or d = 6 – 46 d = 8 or – 40 Then, For a = -2 and d = 8, the A.P is -2, 6, 14 For a = 46 and d = -40, the A.P is 46, 6, -34 ∴ The numbers are – 2, 6, 14 or 46, 6, – 34 |
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