Question

Find the sum of first 25 terms of an A.P whose nth term is given by an = 2 – 3n.

Answer 1

Answer: an = 2 – 3n

a1 = 2 - 3*1

a1 = 2-3

a1 = (-1),   d=(-3)

Sn = (n/2) (2a + (n-1)d)

S25 = (25/2) (2(-1) + (-1-1)(-3)

S25 = 25/2 * 4

S25  = 25*2

S25 = 50

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