Identities.
#color(red)bb(cotx=cosx/sinx)#
#color(red)bb(sin2x=2sinxcosx)#
#color(red)bb(sin^2x+cos^2x=1)#
#(1+cos^2x/sin^2x)(2sinxcosx)=2#
Add fractions:
#(sin^2x+cos^2x)/sin^2x(2sinxcosx)=2#
#1/sin^2x(2sinxcosx)=2#
#(2sinxcosx)/sin^2x=2#
#(2sinxcosx)=2sin^2x#
#2sinxcosx-2sin^2x=0#
Factor:
#sinx(2cosx-2sinx)=0#
#sinx=0#
#x=arcsin(sinx)=arcsin(0)=>x=pik#
#2cosx-2sinx=0#
#(2sinx)/(2cosx)=0#
#tanx=0#
#x=arctan(tanx)=arctan(0)=>x=pik#
#x=pik#
#k in ZZ#