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If the sum and product of the first three terms in an A.P. are 33 and 1155, respectively, then a value of its 11th term is : (1) –25 (2) –35 (3) –36 (4) 25 |
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Answer» Correct option (1) –25 Explanation: Let the three numbers in A.P. are a – d, a, a + d given that : a – d + a + d = 33 ⇒ a = 11 and (a – d)(a)(a + d) = 1155 ⇒ a(a2 – d2 ) = 1155 ⇒ 11(121 – d2 ) = 1155 ⇒ d2 = 16 ⇒ d = ±4 If d = 4 then first term a – d = 7 If d = –4 then first term a – d = 15 T11 = 7 + 10(4) = 47 or T11 = 15 + 10(–4) = –25 |
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