Ответ:

-sin b cos a

Объяснение:

Verified answer

[tex]\displaystyle\bf\\\frac{Sin\alpha Sin\beta -Cos(\alpha -\beta )}{Ctg\beta } =\frac{Sin\alpha Sin\beta -(Cos\alpha Cos\beta +Sin\alpha Sin\beta )}{Ctg\beta }=\\\\\\=\frac{Sin\alpha Sin\beta -Cos\alpha Cos\beta -Sin\alpha Sin\beta }{\frac{Cos\beta }{Sin\beta } } =-\frac{Cos\alpha Cos\beta \cdot Sin\beta }{Cos\beta } =\\\\\\=-Cos\alpha Sin\beta[/tex]