Answer:
The relationship between the two is that they are equal.
Explanation:
Since y = cosx is a even function, that means that cosx = cos(-x). Therefore, cos 90 degrees = cos -90 degrees.
We can also test this out:
cos 90 = 0
cos -90 = cos 270 = 0
Therefore, this came to the same conclusion as our first solution.
I hope this helps! :)