How do you find the cosine of $315^circ$ ?

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Answer 1 · 2017-01-19T06:33:22

$cos(315^@)=1/sqrt(2)$

First notice that $315^@$ is $45^@$ below the x-axis

$315^@=360^@-45^@$

Because of this it is in the 4th quadrant, and since $cos(x)$ corresponds to x values it is positive there.

then

$cos(315^@)=cos(-45^@)=cos(45^@)=1/sqrt(2)$

How do you find the cosine of 315^circ315^circ?