Q25 of 178 Page 559

The sum of first 16 terms of the AP 10, 6, 2, ... is

Here, first term = 10


Common difference = d = 6 - 10 = - 4


Sum of first n terms of an AP is


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


∴ S16 = [2(10) + (16 - 1)(-4)]


= 8 × [20 - 60]


= 8 × (-40)


= - 320


Thus, sum of 16 terms of this AP is - 320.

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