how do you solve problems like: cos[arctan(-1)] ?? thanks everyone
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
Notice that if you used the other angle, your answer would be
So you check what domain you want your answer to be in.