Помогите пожалуйста!!!

Решите задачу:

$\frac{cos^2 \beta -ctg^2 \beta +1}{sin^2 \beta +tg^2 \beta -1} = \frac{cos^2 \beta -\frac{cos^2 \beta }{sin^2 \beta }+1}{sin^2 \beta +\frac{sin^2 \beta }{cos^2 \beta }-1} =\\\\= \frac{(cos^2 \beta \cdot sin^2 \beta -cos^2 \beta +sin^2 \beta )\cdot cos^2 \beta }{sin^2 \beta \cdot (sin^2 \beta \cdot cos^2 \beta +sin^2 \beta -cos^2 \beta )} = \frac{cos^2 \beta }{sin^2 \beta } =ctg^2 \beta$