To find the angle between two points, draw a right triangle from the
points. Label the angle as θ (theta). Label the sides of the triangle as
opposite, adjacent, and hypotenuse. Example using the points (0, 0) and
(4, 3):

Use the trigonometric functions to calculate θ. The three main
trigonometric functions are sine, cosine, and tangent. Each of them can
be used to calculate an angle in a right triange by taking the ratios of
the different sides of the triangle:

In this example, the opposite and adjacent sides are known, so use the
tangent function to calculate the angle:

To solve for θ, do the inverse tangent to both sides, also known as the
arctangent:

Plug that into a computer to get the value of the angle.