Question

Решите уравнение cosx-cos2x=1

Answer 1

$cosx-(2cos^{2}x -1)=1\\-2cos^{2}x+cosx+1=1\\2cos^{2}x-cosx=0\\cosx(2cosx-1)=0\\cosx=0\\x_{1} =\frac{\pi }{2} + 2\pi n, n e z\\x_{2} =-\frac{\pi }{2} + 2\pi n, n e z$

или

$2cosx-1=0\\cosx=\frac{1}{2} \\x_{3} =\frac{\pi}{3} + 2\pi n, n e z\\x_{4} =-\frac{\pi}{3} + 2\pi n, n e z$