Two variables are said to have a direct variation or proportional relationship if it can be represented by y = kx, where k is a constant.
Comparing this with the equation of a straight line y = mx + b, where m is the slope of the line and b is the y intercept (value of y when x = 0), We can tell if the say that the graph of a direct variation or proportional relationship is a straight line with no y intercept (b = 0, that is it passes through the origin).
