Question

Даю 60 баллов за одно задание, помогите ​

Answer 1

Ответ:

$\frac{ \sin {}^{2} ( \alpha ) }{ \sin {}^{2} ( \alpha ) - 1 } \times {ctg}^{2} \alpha - \cos {}^{2} ( \alpha ) = \\ = \frac{ { \sin }^{2} (\alpha )}{ - (1 - \sin {}^{2} ( \alpha )) } \times {ctg}^{2} \alpha - \cos {}^{2} ( \alpha ) = \\ = - \frac{ \sin {}^{2} ( \alpha ) }{ \cos {}^{2} ( \alpha ) } \times {ctg}^{2} \alpha - \cos {}^{2} ( \alpha ) = \\ = - {tg}^{2} \alpha \times ctg \alpha - \cos {}^{2} ( \alpha ) = \\ = - 1 - \cos {}^{2} ( \alpha ) \\ \\ - 1 - \cos {}^{2} ( \frac{\pi}{4} ) = - 1 - { (\frac{ \sqrt{2} }{2} )}^{2} = \\ = - 1 - {( \frac{1}{ \sqrt{2} }) }^{2} = - 1 - \frac{1}{2} = - 1.5$