In a proportional relationship why must the graph of the line always go through the origin (0,0)? explain?

We know that, two quantities are proportional when they vary directly with each other.

i.e. quantities x and y are proportional when they have the relation y = kx, where k is any constant called constant of proportionality.

Since, the quantities are in relation y = kx.

So, for x = 0 we get that the value of y = 0.

As, the point ( 0,0 ) satisfies this relation i.e. it is a solution of y =  kx.

Hence, in proportional relationship, the graph will pass through ( 0,0 ).