Q57 of 84 Page 5

How many terms of the A.P.must be taken so that their sum is 636? (CBSE 2017)

Sn = [2a + (n – 1) d]

636 = [2(9) + (n – 1) 8]


636 = n [9 + 4n -4]


636 = 5n + 4n2


4n2 + 5n – 636 = 0


n = 12 or n = (not possible)

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