Question

The sum of first 3 terms of the A.P. Whose nth term is given by a, = 2n + 1 is​

Answer 1

Step-by-step explanation:

we have : nth term =2n+1 this implies a =2.1+1=3 , a2= 2.2+1 = 5 a3=2.3+1=7 so a(first term)=3 and d(common difference) =5-3=2 now according to question, S3=n/2[2a+(n-d) ] now S3 =3/2(6+4) and S3 will be 15.

Answer 2

Answer:

15

Step-by-step explanation:

Solution:

Given :

• nth term , a(n) = 2n + 1

To find :

• Sum of first three terms , S(3) = ?

We have ;

nth term , a(n) = 2n + 1

Thus,

1st term , a(1) = 2×1 + 1 = 2 + 1 = 3

2nd term , a(2) = 2×2 + 1 = 4 + 1 = 5

3rd term , a(3) = 2×3 + 1 = 6 + 1 = 7

Sum of first n terms is given as ;

S(n) = a(1) + a(2) + a(3) + . . . + a(n)

Therefore,

Sum of first three terms will be ;

=> S(3) = a(1) + a(2) + a(3)

=> S(3) = 3 + 5 + 7

=> S(3) = 15

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