34+1516+6364+............to n terms =
We have,
34+1516+6364+............to n terms
=22-122+24-124+26-126+......to n terms
=1-122+1-124+1-126+........to n terms
=n-122+124+126+........to n terms
=n-1221-122n1-122
=n-131-4-n=n+4-n3-13