Solve: tanxtan2x+tan2xtan3x+tan3xtan4x+....n terms =
tanx=tan(2x−x)=tan2x−tanx1+tan2xtanx ∴T1=tan2xtanx=cotx(tan2x−tan1)−1 ∴T2=cotx(tan3x−tan2x)−1 etc. ∴Sn=cotx[tan(n+1)x−tanx]−n =cotxtan(n+1)x−1−n