3) Geometric Interpretation of Direct Variation. The equation \(y = kx\) is a special case of linear equation (\(y=mx+b\)) where the y-intercept equals 0. (Note: the equation \(y = mx + b\) is the slope-intercept form where m is the slope and b is the y-intercept). Anyway, a straight line through the origin (0,0) always represents a direct variation between y and x. The slope of this line is the constant of variation.