The equations of lines are of the following forms: 1 - Slope intercept form. y = m x + b. ... 2 - Point Slope Form. y - y 1 = m (x - x 1). ... 3 - Equation of a Vertical Line. x = k , where k is a constant. ... 4 - Equation of a Horizontal Line. y = k , where k is a constant. ... 5 - General Equation of a Line.