Question

cos 4x = - 1; 2) 2cos2х – 1 = 0. срочно у меня мало времени!!!​

Answer 1

$1)Cos4x=-1\\\\4x=\pi+2\pi n,n\in Z\\\\x=\frac{\pi }{4}+\frac{\pi n }{2},n\in Z\\\\\\2)2Cos2x-1=0\\\\2Cos2x=1\\\\Cos2x=\frac{1}{2}\\\\2x=\pm arcCos\frac{1}{2}+2\pi n,n\in Z\\\\2x=\pm \frac{\pi }{3}+2\pi n,n\in Z\\\\x=\pm\frac{\pi }{6}+\pi n,n\in Z$