Sin5a*cos4a+cos(пи/2-a)-cos5a*sin4a
Sin5a*cos4a+cos(пи/2-a)-cos5a*sin4a=sin5a*cos4a+sina-cos5a*sin4a= (sin5a*cos4a-cos5a*sin4a)+sina=sin(5a-4a)+sina=sina+sina=2sina