Find the angle between two points Given two points A and B, find the angle from line AO to line BO about point O where O is the origin ((0,0)). Additionally, the angle may be positive or negative depending on the positions of the points (see examples). Input will be points A and B, and may be given in any convenient form. Output will be the angle in degrees (but it is positive if AO is rotated counter-clockwise about the origin to get BO and negative if it is rotated clockwise). If the angle is 180 degrees you may return a negative or positive output. Similarly, the angle can be the positive or negative version of the same angle (90 deg is equal to -270 deg). Examples:


Input: A(5,5) B(5,-5) Output: -90 (AO is rotated -90 degrees to get BO).
Input: A(5,-5) B(5,5) Output: 90 (AO is rotated 90 degrees to get BO).


This is code-golf, so shortest code in bytes wins!
TI-BASIC, 13 bytes
For TI-83+/84+ series calculators.
Degree
Input Y
min(ΔList(R►Pθ(Ans,∟Y

To use this program, enter the list {x1,x2} through the Ans variable, and {y1,y2} at the prompt.