Question

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

Answer 1

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

Explanation:

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)`