Question

is this right? isn't the Directly proportional equation this. x=(1/k)y

Answer 1

It's y=kx. But 'k' is any constant. So my 'k' can easily be 1/(your k). The key is that when 'x' or 'y' increases by some factor, the other one also increases, by some constant multiple of the same factor. If so, then they're proportional.