Question

. The sum of first 18 terms of an AP whose nth term is 3 − 2n is

Answer 1

Answer:

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Step-by-step explanation:

Given that nth term of an ap is 3 - 2n i.e.

an = 3-2n

So,

a1 = 3-2 = 1

a2 = 3-4 = -1

a3 = 3-6 = -3

a4 = 3-8 = -5

a5  = 3-10 = -7

So, it give that

first term = a = 1

&

common difference =

d = -3.

Now , we have to find sum of its first 18 terms

So,

n=18.

S18 = 18/2 (2a+17d)

= 9(2-51)

= 9 * (-49)

= -441

so sum of its first 18 terms is equals to -441 .