Question

$sqrt{2}cos2x= -1$

Answer 1

$sqrt{2}cos2x=-1\\cos2x=- frac{1}{ sqrt{2} }\\cos2x=- frac{ sqrt{2} }{2} \\2x=б frac{3 pi }{4}+2 pi n, nin Z\\x=б frac{3 pi }{8}+ pi n, nin Z$

Answer 2

спс