Question

it the nth term of an AP is (5n+1) then the sum of it first three terms is :a)33b)15c)12d)21​

Answer 1

Answer :

33

Solution :

• Given : nth term , a(n) = 5n + 1
• To find : Sum of 1st terms , S(3) = ?

We have ;

nth term , a(n) = 5n + 1

Thus ,

First term , a(1) = 5×1 + 1

a(1) = 5 + 1

a(1) = 6

Also ,

Second term , a(2) = 5×2 + 1

a(2) = 10 + 1

a(2) = 11

Now ,

Third term , a(3) = 5×3 + 1

a(3) = 15 + 1

a(3) = 16

Now ,

The sum of the first three terms will ;

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

=> S(3) = 6 + 11 + 16

=> S(3) = 33

Hence , S(3) = 33 .