Question

Вычислите sin α , если cos α=4/5 и 3 π/2 < α < 2 π

Answer 1

Ответ:

$cos\alpha =\dfrac{4}{5}\\\\\dfrac{3\pi }{2}<\alpha <2\pi \ \ \to \ \ \ sin\alpha <0\\\\sin^2\alpha =1-cos^2\alpha \ \ ,\ \ sin^2\alpha =1-\dfrac{16}{25}=\dfrac{9}{25}\\\\sin\alpha =-\dfrac{3}{5}$