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Five numbers are in A.P. with common difference ≠ 0. If 1st, 3rd and 4th terms are in G.P., then which term is always zero? |
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Answer» Let the five numbers in A.P. be a – 2d, a – d, a, a + d, a + 2d. Since 1st, 3rd and 4th terms are in G.P. (t3)2 = t1 . t4 ⇒ a2 = (a – 2d) (a + d) ⇒ a2 = a2 – ad – 2d2 ⇒ – ad = 2d2 ⇒ a = – 2d (∵ d ≠ 0) ⇒ a + 2d = 0 ⇒ t5 = 0 ∴ 5th term is always zero. |
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