Angle#4254
There are two points in the plane. We can draw two segments from the origin to each of these points. Calculate the angle between these two segments.
The angle should be given in radians and must be less than . Be careful, it is an angle, not an angel.
The first line contains a single integer , indicating the number of test cases. Each test case consists of four integers X_a, Y_a, X_b, Y_b (-10000 \le X_a, X_b, Y_a, Y_b \le 10000), indicating the coordinates of the two points. You may assume neither of the points coincides with the origin.
For each test case, output the angle rounded to three fractional digits.
Мысал 1