Question

If nth term of an ap is 2n+1. What is the sum of first three terms

Answer 1

Answer:

Step-by-step explanation:

For an A.P.

nth term=2n+1

Therefore

1st term=2×1+1

=3

2nd term=2×2+1

=5

3rd term=2×3+1

=7

Sum of first 3 terms=1st term+2nd term+3rd term

=3+5+7

=15

Alternative method

You can find the common difference by subtracting 1st term from 2nd term.

Then you will have

a=3

d=2

n=3

Then substitute it in the formula of Sn.

Hope it helps.

Answer 2

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