Question

find the sum of the first 20 terms of series 1+ 2+ 3+ ​

Answer 1

Answer:

210 is the answer........

Answer 2

question

we have to find sum of the first 20 terms of series

1+2+3+....

solution

given series : 1+2+3...

we can observe that this series in Ap

with common difference,d = 1

first term = 1

n of terms = 20

l = an = a + (n -1 ) d = 1+19d = 20

sum of n terms of ap = (n/2 )(a+ l )

Sn =( 20/2)(1+20)

= 10× 21

= 210

therefore sum of first 20 terms of series 1+2+3..

is 210

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