Answer :

Here, second term = a2 = 14

Third term = a3 = 18


Common difference = a3 - a2 = 18 - 14 = 4


Thus first term = a = a2 - d = 14 - 4 = 10


Now, Sum of first n terms of an AP is given by


Sn = [2a + (n - 1)d]


Sum of first 51 terms is given by:


S51 = [2(10) + (51 - 1)(4)]


= (51/2) × [20 + 200]


= (51/2) × 220


= (51) × 110


= 5610


S51 = 5610


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