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Cos(2x)=-(√2)/2 Can anyone help me solve this?

Quote: Originally Posted by ssmh Cos(2x)=-(√2)/2 Can anyone help me solve this? I kind of sleepy so hopefully I don't make a mistake lol Ok so you know cos is negative in the 2nd and 3rd quadrant. Also at 135 degrees and 225 Now just divide 135 and 225 by 2 and it will give you your answer