Explanation:
Any linear equation in the form y = mx+b has a constant rate of change, and that rate of change is the slope m. If b = 0, then it turns into y = mx. Here m is the constant of proportionality. Direct proportion equations always go through the origin. If b is nonzero, then y = mx+b will not be proportional.
So for example, y = 2x is proportional while y = 2x+1 is not proportional.
