If an angle θ in standard position intersects the unit circle in a given position (x,y), we can say that:
So, in 1, we got this intercection in
So,
In 2, to find the cossine, we first need the hypotenuse. The hypotenuse, in this case, is the radius fo the circle, which is one because it is a unit circle. So, we must do the adjacent leg divided by the hypotenus. The adjacent leg is equivalent to the x of the coordinate, so, for:
We got:
In 3, we just have to calculate