Fewpal
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Sum of first n terms of A.P will be n

Explanation :
n1=7
Sn=49
we know that S
n = n/2{2a+(n-1)d}

thus,
Sn1=7/2(2a+6d)=49
    =14a+42d=98     ... (1) x17

n2=17
Sn2=289

Sn2=17/2(2a+16d)=289
     =34a+272d=578     ....(2) x7
from eq 1 & 2
238a +714d =1666    ....(3)
238a +1904d=4046    .....(4)

subtracting (4) -(3)
1190d=2380
    d=2
    a=1

sum of n terms will be 
 Sn = n/2{2a+(n-1)d}
Sn = n
 

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