(cosa+cos3a)/sin2a+(sina+sin3a)/(1+cos2a)=?

=2cos2a*cosa/(2sina*cosa)+2sin2a*cosa/(1+2cos²a-1)=cos2a/sina+sin2a/cosa=(1-2sin²a)/sina+2sina*cosa/cosa=1/sina-2sina+2sina=1/sina=Coseca