Найдите tg a ,если (7sin a + 13cos a) / (5sin a - 17cos a) = 3

7sina+13cosa=15sina-51cosa8sina=64cosasina=8cosatga=8 

sin70 cos40 - sin160 sin40=sin70 cos40 - sin(90+70) sin40=sin70 cos40 - cos70sin40=sin(70-40)=sin30=1/2

sin20 sin 80 +sin 110 cos 80=sin20 sin 80 +sin(90+20) cos 80=

sin20 sin 80 +cos20 cos 80=cos(80-20)=cos60=1/2

тогда

(sin70 cos40 - sin160 sin40)/(sin20 sin 80 +sin 110 cos 80)=(1/2)/(1/2)=1

sin 187= -0.9  < 0

cos 215= 0.1  >   0

tg 80 =  9 > 0