Question

the aum of first 20 natural number​

Answer 1

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Answer 2

Answer:

We have to find the sum n terms of the AP 1,2,3,...

Here

a=1,d=1.

Therefore, Required sum Sn=2n[2a+(n−1)d]=2n[2×1+(n−1)×1]

⇒Sn=2n[2+n−1]

⇒Sn=2n(n+1)                        ...(1)

Put n=20 in (1), we get

S20=220(20+1)=210