Cos(2x)=-(√2)/2
Can anyone help me solve this?
I kind of sleepy so hopefully I don't make a mistake lol
$\displaystyle \cos{(2x)}=-\frac{\sqrt{2}}{2}$
Ok so you know cos is negative in the 2nd and 3rd quadrant.
Also $\displaystyle \cos{x} = -\frac{\sqrt{2}}{2}$ at 135 degrees and 225
Now just divide 135 and 225 by 2 and it will give you your answer
$\displaystyle 67.5 + 360n$
$\displaystyle 112.5 + 360n$
$\displaystyle n = 0,\pm 1, \pm 2,...$