Pre-Calc: Vector Angle

You have two 2D vectors and you want the angle on the plane between them.

-- Vector Angle --

:Input "X1: ",A

:Input "Y1: ",B

:Input "X2: ",C

:Input "Y2: ",D

:Degree

:cos^-1(((AC)+(BD))/(√(A²+B²)√(C²+D²)))→M

:Disp M