Angle Between Two Lines

We often think of lines as having a direction, and the angle between them is simply the measure of how much one line must be rotated to align with the other. This angle is uniquely determined by the slopes of the two lines, giving us a clean algebraic way to capture a geometric idea. Instead of measuring with a protractor, we can compute the acute angle using the slopes $m_1$ and $m_2$, which is especially useful when the lines are not drawn to scale. Understanding this connecti …