Question

if the sum of first 7 terms of an A.P. is 49 and that of 17 terms is 289, find the sum of first n terms.

Answer 1

let a be first term and d be common difference

7/2 ( 2a+ 6d) = 49

17/2( 2a + 16 d) = 289

2a + 6d = 14

2a + 16 d= 34

10 d= 20
d=2

2a + 12 = 14.
a= 1


Sum of first n terms = n/2 ( 2 + (n-1)2)

Answer 2

Hey !!! ^_^

Here is your answer

⬇️⬇️⬇️⬇️⬇️⬇️

In attachment
Given

The sum of first 7th term of an ap is 49...

And The sum 17 term of an ap is 289 ...

means

S7 = 49
and

S17 = 289


Using the Formula oF ..

Sum of term of Ap ...

That is

Sn = n/2{2a + (n- 1)d}..



I HOPE IT WILL HELP YOU

Thank you

☺️