Question

Как решить эту систему?

$\cos(x) \cos(y) = \frac{1}{4}$
$\sin(x) \sin(y) = \frac{3}{4}$

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Answer 1

$\sf \displaystyle \left \{ {{\cos x\cos y=\frac{1}{4}} \atop {\sin x \sin y = \frac{3}{4}}} \right. |+\left \{ {{\cos x\cos y-\sin x \sin y=\frac{1}{4}-\frac{3}{4}} \atop {\cos x\cos y+\sin x\sin y =\frac{1}{4}+\frac{3}{4}}} \right. \\\\ \left \{ {{\cos (x+y)=-\frac{1}{2}} \atop {\cos (x-y)=1}} \right. \left \{ {{x+y=\pm \frac{2\pi}{3}+2\pi n,n\in Z} \atop {x-y=2\pi n,n\in Z}} \right.$

$\sf\displaystyle \left \{ {{2x=\pm \frac{2\pi}{3}+4\pi n,n\in Z} \atop {2y=\pm \frac{2\pi}{3}}} \right. \left { {{|:2} \atop {|:2}} \right. \left \{ {{x=\pm\frac{\pi}{3}+2\pi n,n\in Z} \atop {y=\pm \frac{\pi}{3}}} \right.$