Question

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

Answer 1

Answer:

n^2

Step-by-step explanation:

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

7=a+3d------1

289=17/2[2a+16d]

17=a+8d-----2

Solving 1 and 2

a+3d=7

a+8d=17

==== - 5d=-10

d=2

Sub in 1 or 2 to get the value of a which is 1

Now

Sn=n/2[2(1)+(n-1)2]

=n^2

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Hope it helps