Q43 of 84 Page 5

The nth term of an AP is given by (- 4n + 15). Find the sum of first 20 terms of this AP? (CBSE 2013)


an = (- 4n + 15)

a1 = -4(1) + 15
    = -4 + 15
    = 11

a2 = -4(2) + 15
    = -8 + 15
    = 7

d = 7 - 11
 = -4

Now, we have a =11, d = - 4




= 10[22-76]

= 10(-54)

= -540

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