Question

Find the sum of first 20 terms of an AP, whose nth term is 9m-1

Answer 1

Answer:

1550

Step-by-step explanation:

the the first term of the AP

a1= 9(1)-1= 8

the 28th term of AP

a2= 9(20)-1= 179

the common difference d of the AP is

a1-a2=[9(2)-1]- 8= 9

sum of the first 20 terms of the AP

s20= 20/2(-2(8)+(20-1)9) = 1550

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