Question

How to find the angle between two lines given their slopes?

Answer 1

Tan(tan−1(yx)−θ) is the slope m. Then use "point slope formula" (if you want an equation of the line, that is...) Labeling the origin "O" and the point (x,y) "P", the segment ¯OP makes an angle of tan−1(yx) with the positive x-axis