If range of \( f(\theta) = \dfrac{\sin^4 \theta + 3\cos^2 \theta}{\sin^4 \theta + \cos^2 \theta} , \\ \theta \in \mathbb{R} \) is \( [\alpha, \beta] \), then the sum of the infinite G.P., whose first term is \( 64 \) and the common ratio is \( \dfrac{\alpha}{\beta} \), is equal to ______.
