Since there's been no reply, let's get started by observing that we must have:
$$r=\alpha\beta$$
Now, to express \(\alpha\) and \(\beta\) in terms of \(p\) and \(q\) I would look at:
$$\alpha^2-p\alpha+r=\frac{\alpha^2}{4}-q\frac{\alpha}{2}+r$$
$$\beta^2-p\beta+r=4\beta^2-2q\beta+r$$
Solve the first equation for the non-zero value of \(\alpha\) and solve the second equation for the non-zero value of \(\beta\)...what do you find?