(3*cos*(п-B) sin*(п/2+ В))/(cos*(В+3*п))

[latex] \frac{3cos( \pi - \beta )sin( \frac{ \pi }{2}+ \beta ) }{cos(3 \pi + \beta )} = \frac{-3 cos\beta*cos \beta }{-cos \beta } =3cos \beta [/latex]