Question

Умоляю хелпаните!! (задание на скрине)

Answer 1

$1+tg ^{2} \alpha = \frac{1}{Cos ^{2} \alpha } \\\\Cos ^{2} \alpha = \frac{1}{1+tg ^{2} \alpha } = \frac{1}{1+ \frac{81}{144} } = \frac{1}{ \frac{225}{144} }= \frac{144}{225} \\\\Cos \alpha = \sqrt{ \frac{144}{225} } = \frac{12}{15}$