# tan(x/2) *(1+secx)*(1+sec2x)*(1+sec2^2x)*...(1+sec2^nx)#
#=tan(x/2)*(1+cosx)/cosx*(1+sec2x)*(1+sec2^2x)*...(1+sec2^nx)#
#=sin(x/2)/cos(x/2)*(2cos^2(x/2))/cosx*(1+sec2x)*(1+sec 2^2x)*...(1+sec2^nx)#
#=(2sin(x/2)cos(x/2))/cosx*(1+sec2x)*(1+sec 2^2x)*...(1+sec2^nx)#
#=sinx/cosx*(1+cos2x)/cos(2x)*(1+sec 2^2x)*...(1+sec2^nx)#
#=sinx/cosx*(2cos^2x)/cos(2x)*(1+sec 2^2x)*...(1+sec2^n x)#
#=(2sinxcosx)/cos(2x)*(1+sec 2^2x)*...(1+sec 2^nx)#
#=(sin2x)/cos(2x)*(1+sec 2^2 x)*...(1+sec2^nx)#
#=tan2x*(1+sec 2^2x)*...(1+sec2^nx)#
#=.............#
#=.............#
#=.............#
#=tan(2^n x)#