# how do you solve problems like: cos[arctan(-1)] ?? thanks everyone

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1. Tangent of what angle is -1?

2. What is cosine of this angle?

The tangent function is like the slope of a radius on the unit circle. There are two that have a slope of -1: `135^o` and `315^o`

Let's just use the first one: `135^o` or `(3pi)/4` radians.

Take the cosine (visualize the adjacent and hypotenuse: `-sqrt(2)/2` and `1` ), and your answer is

`-sqrt(2)/2`

Notice that if you used the other angle, your answer would be

`sqrt(2)/2`

So you check what domain you want your answer to be in.

in the problem all i was given was this, and it wants me to use the properties of inverse functions......i dont really understand it yet...