Question

$frac{ { tan }^{2} alpha -1 }{ cos(2 alpha ) } \ \ frac{4 tan( alpha ) (1 - { tan }^{2}) }{1 + { tan }^{2} alpha }$
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Answer 1

б) $frac{tg^{2}a - 1}{cos2a } = frac{frac{sin^{2}a - cos^{2}a}{cos^{2}a} }{cos2a } = - frac{frac{cos2a}{cos^{2}a} }{cos2a} = - frac{1}{cos^{2}a} = - 1 - tg^{2}a$