Question

The sum of the first 20 terms of an ap whose first term is 5 find the common difference is 4 is

Answer 1

5,9,13,17,21,25,29,33,37,41,45,49,53,57,.......

Answer 2

$\huge{\sf{\boxed{\boxed{Answer:-860}}}}$

Question

The sum of the first 20 terms of an ap whose first term is 5 . Find the common difference is 4 .

Given that :-

First term if an AP = a = 5

Common difference = d = 4

No. of terms = n = 20

Formula to find the sum is n/2 (a + l) where l is the last term or An.

so first of all, we needa find the 20th term.

We know that,

An = a + (n - 1)d

An = 5 + (20 - 1)4

An = 5 + (19)4

An = 5 + 76

An = 81

The 20th term of the AP is 81.

Therefore sum of first 20 terms :-

= n/2 (a + An)

= 20/2 (5 + 81)

= 10 × 86

= 860

Hence, the sum of first 20 terms is 860