Sin4a+sin5a+sin6a деленое cos4a+cos5a+cos6a народ вопрос жизни и сметри

(sin4a+sin5a+sin6a)/(cos4a+cos5a+cos6a)=

=(2sin((4a+6a)/2)*cos((6a-4a)/2)+sin5a)/(2cos((4a+6a)/2)*cos((6a-4a)/2)+cos5a)=

=(2sin5a*cosa+sin5a)/(2cos5a*cosa+cos5a)=

=(sin5a(2cosa+1))/(cos5a(2cosa+1))=sin5a/cos5a=tg5a