#cos4theta-3tan2theta+sin2theta#
#=1-2sin^2 2theta-3tan2theta+sin2theta#
#=1-2sin^2 2theta +sin2theta-3tan2theta#
#=1+2sin2theta-sin2theta-2sin^2 2theta-3tan2theta#
#=(1+2sin2theta)-sin2theta(1+2sin2theta)-3tan2theta#
#=(1+2sin2theta)(1-sin2theta)-3tan2theta#
#=(1+(4x)/(1+x^2))(1-(2x)/(2+x^2))-(6x)/(1-x^2)#
#color(red)("where " x=tantheta)#