How to find the rotation angle of an object so that it looks at 2 points with two axes?

Question

Mathematics

There are 2 points in space. If we take them as the legs of a triangle, then the angle will be 90.
There is an object in whose space two direction vectors are drawn with a similar angle (90*). You need to find the angle of rotation of the object so that these two vectors look at the points.
It's all in two dimensions.
At the input we have the coordinates of 2 points. Angle exit.

Answer 1

One point is enough. The angle between the OX axis and the direction to this point is arctg(y/x).

Answer 2

Difference between 45° and line angle A1-A2