Question

Как это решили??????????

Answer 1

tg(180-a) = sin(180-a)/cos(180-a) = (sin(180)*cos(a) - sin(a)*cos(180))/(cos(180)*cos(a) + sin(180)*sin(a))
cos(180) = -1
sin(180) = 0
-(-sin(a))/(-cos(a)) = -tg(a)

Answer 2

$\displaystyle tg(180- \alpha )= \frac{sin(180- \alpha)}{cos(180- \alpha)}= \frac{sin \alpha }{(-cos \alpha )}=- \frac{sin \alpha }{cos \alpha }=-tg \alpha$