Question

if the sum of first 7 terms of an Ap is 49 and that of 17 terms is 239, find the first n terms​

Answer 1

Answer:

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Answer 2

Answer:

Sum of n terms=n²

Step-by-step explanation:

if the sum of first 7 terms of an Ap is 49 and that of 17 terms is 289, find the sum of first n terms​

S7=49=7/2 ( 2a+6d)

2a+6d=49*2/7=14

2a+6d=14....................(1)

S17=239=17/2( 2a+16d)

2a+16d=289*2/17=17*2=34

2a+16d=34..................(2)

subtract (1) from(2)

10d=20,d=2

from(1)2a+12=14

2a=2,a=1

Sn=n/2( 2*1+(2(n-1) }

=n/2 ( 2+2n-2)

=n/2 ( 2n

=n²