Упростить

cos(180+a)*cos(-a)[tex] \frac{x}{y} [/tex]sin(-a)*sin(90+a)=

sin(П-a)*cos(2П-a)[tex] \frac{x}{y} [/tex]tg(П-a)*cos(П-a)=

[tex] \frac{cos(180+ \alpha )*cos(- \alpha )}{sin(- \alpha )*sin(90+ \alpha )} = \frac{-cos \alpha *cos \alpha }{-sin \alpha *cos \alpha } =ctg \alpha [/tex]

[tex] \frac{sin( \pi - \alpha )*cos(2 \pi - \alpha )}{tg( \pi - \alpha )*cos( \pi - \alpha )} = \frac{sin \alpha *cos \alpha }{-tg \alpha *(-cos \alpha )} = \frac{sin \alpha }{tg \alpha } =cos \alpha [/tex]