Please solve the 6 th problem.
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Q.6. The sum of first 7 terms of an A.P. is 49 and that of first 17 terms of it is 289. Find the sum of first n terms.

Here is the solution of your asked query:

Given that,

S₇ = 49

S₁₇ = 289

7 = (a + 3d)

a + 3d = 7 (i)

Similarly,

17 = (a + 8d)

a + 8d = 17 (ii)

Subtracting equation (i) from equation (ii),

5d = 10

d = 2

From equation (i),

a + 3(2) = 7

a + 6 = 7

a = 1

= n<sup>2

Regards</sup>