#tana=tan/_CPA=(AC)/(AP)=(1/2AB)/(nAB)=1/(2n)#
#tan(a+b)=tan/_BPA#
#=>(tana+tanb)/(1-tanatanb)=(AB)/(AP)=1/n#
#=>(ntana+ntanb=(1-tanatanb)#
#=>(nxx1/(2n)+ntanb)=(1-1/(2n)tanb)#
#=>1/2+ntanb=1-1/(2n)tanb#
#=>ntanb+1/(2n)tanb=1-1/2#
#=>(n+1/(2n))tanb=1/2#
#=>((2n^2+1)/(2n))tanb=1/2#
#=>tanb=n/(2n^2+1)#