Найдите значение выражения \(\displaystyle \frac{\cos^2\alpha - \mathrm{ctg^2}\,\alpha + 1}{\sin^2\alpha + \mathrm{tg^2}\,\alpha - 1}\), если \(\mathrm{ctg}\,\alpha = 7\).
\[\begin{gathered} \frac{\cos^2\alpha - \mathrm{ctg^2}\,\alpha + 1}{\sin^2\alpha + \mathrm{tg^2}\,\alpha - 1} = \frac{\frac{\cos^2\alpha\cdot\sin^2\alpha}{\sin^2\alpha} - \frac{\cos^2\alpha}{\sin^2\alpha} + \frac{\sin^2\alpha}{\sin^2\alpha}}{\frac{\cos^2\alpha\cdot\sin^2\alpha}{\cos^2\alpha} + \frac{\sin^2\alpha}{\cos^2\alpha} - \frac{\cos^2\alpha}{\cos^2\alpha}} = \frac{\frac{\cos^2\alpha\cdot\sin^2\alpha - \cos^2\alpha + \sin^2\alpha}{\sin^2\alpha}}{\frac{\cos^2\alpha\cdot\sin^2\alpha - \cos^2\alpha + \sin^2\alpha}{\cos^2\alpha}} =\\= \frac{\cos^2\alpha\cdot\sin^2\alpha - \cos^2\alpha + \sin^2\alpha}{\sin^2\alpha}\cdot\frac{\cos^2\alpha}{\cos^2\alpha\cdot\sin^2\alpha - \cos^2\alpha + \sin^2\alpha} =\\= \frac{\cos^2\alpha}{\sin^2\alpha} = \mathrm{ctg^2}\,\alpha = 7^2 = 49\end{gathered}\]
Ответ: 49