InterviewSolution
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InterviewSolution
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Decide whether following sequence is an A.P., if so find the 20th term of the progression.-12, -5, 2, 9,16, 23,30,… |
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Answer» i. The given sequence is -12, -5,2, 9, 16, 23,30,… Here, t1 = -1, t2 = -5, t3 = 2, t4 = 9 ∴ t2 – t1 – 5 – (-12) – 5 + 12 = 7 t3 – t2 = 2 – (-5) = 2 + 5 = 7 ∴ t4 – t3 – 9 – 2 = 7 ∴ t2 – t1 = t3 – t2 = … = 7 = d = constant The difference between two consecutive terms is constant. ∴ The given sequence is an A.P. ii. tn = a + (n – 1)d ∴ t20 = -12 + (20 – 1)7 …[∵a = -12, d = 7] = -12 + 19 × 7 = -12 + 133 ∴ t20 = 121 ∴ 20th term of the given A.P. is 121. |
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