Question

Простите выражение.

sin7a+sin3a (дробь) cos7a+cos3a

Answer 1

(sin7a+sin3a)/(cos7a+cos3a)=2sin5a*cos2a/2cos5a*cos2a=sin5a/cos5a=tg5a

Answer 2

Формулы:
sin x + sin y = 2 sin ((x + y)/2) cos ((x - y)/2)
cos x + cos y = 2 cos((x + y)/2) cos ((x - y)/2)

(sin 7a + sin 3a) / (cos 7a + cos 3a) = (2 sin 5a cos 2a) / (2 cos 5a cos 2a) = sin 5x / cos 5a = tg 5a