The equation y = mx + c represents a line with slope m and y-intercept c. This is the most commonly used form because it directly reveals two properties. When comparing two lines y = m1x + c1 and y = m2x + c2: parallel if m1 = m2 (with c1 not equal to c2), coincident if m1 = m2 and c1 = c2, and intersecting otherwise. The x-intercept of this line is -c/m.