Question

The sum of the first 7 term of an AP is 49 and the sum of it's first 17 terms is 289. Find the sum of it's first n terms.

Answer 1

S7=7/2(2a+6d)
49=7a+21d
7=a+3d...........(1)

Now, s17=17/2(2a+16d)
289=17a+136d
17=a+8d..................2

From1and2

5d=10
D=2

Put din 1
A=1

Sum of nth term =n/2(2+n-1)
=n2+n/2

Hope this helps you
Mark as a brainliest

Answer 2

HAIII HERE'S UR ANSWER .