The lines l_{1} and l_{2} have vector equations
r=(\lambda cos\theta)i+(\sqrt{2}\lambda sin\theta)j+4k
r=(\sqrt{2}+\frac{\mu}{\sqrt{2}}sin\theta)i+j+(3+\  mu cos \theta)k
respectively, where \theta is a constant such that 0\leq\theta<\pi, and \lambda and \mu are real parameters.
The points P is on l_{1} and Q on l_{2} are such that PQ is perpendicular to both lines.

Show that for all values of \theta, PQ\leq\sqrt{2}

Thanks you.