Sum of first n terms of A.P will be n2
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 S**n =**n/2{2a+(n-1)d}
S**n =**n2
