cos(a) = x/r
sin(a) = y/r
tan(a) = y/x
In the image at the end, you can see a sketch of the situation, we can model this with a triangle rectangle:
The hypotenuse length is equal to r, the adjacent cathetus to the angle is the x-value, and the opposite cathetus to the angle is the y-value.
Now we can remember the trigonometric relations:
cos(a) = (adjacent cathetus)/(hypotenuse)
sin(a) = (opposite cathetus)/(hypotenuse)
tan(a) = (opposite cathetus)/(adjacent cathetus)
Using what we wrote above, we can rewrite these as:
cos(a) = (adjacent cathetus)/(hypotenuse) = x/r
sin(a) = (opposite cathetus)/(hypotenuse) = y/r
tan(a) = (opposite cathetus)/(adjacent cathetus) = y/x
if you want to learn more about this topic, you can read:
https://brainly.com/question/24297646