Question

ПОМОГИТЕ СРОЧНО !! Дано; $sin alpha = frac{15}{17} : - frac{3 pi }{2} < alpha <-2 pi .$  Найдите $cos alpha$

Answer 1

a∈II четверти 
$sin alpha = frac{15}{17} \ cos alpha =- sqrt{1- frac{225}{289} } = -sqrt{ frac{64}{289} } =- frac{8}{17}$

Answer 2

$sin alpha = frac{15}{17} \ cos alpha = sqrt{1-sin^{2} alpha } cos alpha = sqrt{1-( frac{15}{17})^{2} } = sqrt{ frac{64}{289} } = frac{8}{17} ;- frac{3 pi }{2} < alpha < -2 pi$