Question

here is sum of chap- A.P pls solve it step by step​

Answer 1

now factorise it you will get answer.....

Answer 2

a=2 ; d= 7-2 = 5

Sn = n/2 {2a+(n-1)d}
990 = n/2 {2(2)+(n-1)(5)}
1980 = n {4+5n-5}
1980 = n {5n-1}
1980 = 5n^2 - n
5n^2 - n - 1980 =0
5n^2 - 100n + 99n - 1980 = 0
5n(n - 20) + 99(n - 20) =0
(5n + 99) (n - 20) =0

thus, n - 20 =0
n = 20........(1)
5n + 99 = 0
n = -99/5..........(2)
it is not possible because n refers to the natural number

So, there are 20 terms.

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