Let $C:\ x^{2}+y^{2}=4$ and $C':\ x^{2}+y^{2}-4\lambda x+9=0$ be two circles. If the set of all values of $\lambda$ for which the circles $C$ and $C'$ intersect at two distinct points is $\mathbb{R}\setminus [a,b]$, then the point $(\,8a+12,\ 16b-20\,)$ lies on the curve: