3+5+7+.......ToNTerm
Sn=3+5+7+.......+n
Since above series is an AP with a=3
d=5–3=2
Therefore,
Sn=n22a+(n-1)d=n22×3+(n-1)2=n26+2n-2=n22n+4=n2×2n+2=n(n+2)
Hence, the required answer is n(n+2).