What is Cosine
Let a right-angled triangle ABC with an acute angle α be given, then the cosine of angle α will be the ratio of the adjacent leg to the hypotenuse
cos α = AB/AC .
Also, to determine the cosine of an angle, you can use a circle built in a Cartesian coordinate system, radius R and center at the origin O.
On the circle, mark the point P with coordinates (1; 0), now turn the ray OP by some angle α.
Counterclockwise direction is considered positive, clockwise direction is negative.
The cosine of the angle α will be the ratio of the abscissa of the point XP to the radius of the circle.
cos α = XP/R, if the circle is unit (circle radius = 1), the formula will take the form cos α = XP .