Question

cos a/2 если cos a = - 3/4, π/2

Answer 1

Ответ:

$cosa=-\dfrac{3}{4}\\\\\\cos^2\dfrac{a}{2}=\dfrac{1+cosa}{2}=\dfrac{1-\frac{9}{16}}{2}=\dfrac{7}{32}\\\\\\\dfrac{\pi}{2}<a<\pi \ \ \ \Rightarrow \ \ \ \dfrac{\pi}{4}<\dfrac{a}{2}<\dfrac{\pi}{2}\ \ ,\ \ \ cos\dfrac{a}{2}>0\ \ ,\ \ \ cos\dfrac{a}{2}=+\sqrt{\dfrac{7}{32}}$