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How many terms of the AP 21, 18, 15, … must be added to get die sum 0? |
Answer» AP is 21, 18, 15,… a = 21, d = 18 – 21 = -3 Sum of terms = Sn = 0 (n/2) [2a + (n – 1)d] = 0 (n/2) [2(21) + (n – 1)(-3)] = 0 (n/2) [45 – 3n] = 0 [45 – 3n] = 0 n = 15 (number of terms) Thus, 15 terms of the given AP sums to zero. |
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