Let \( f(x) \) be a positive function and \( I_1 = \int_{-1/2}^{1} 2x\, f\!\big(2x(1-2x)\big)\,dx \) and \( I_2 = \int_{-1}^{2} f\!\big(x(1-x)\big)\,dx \). Then the value of \( \dfrac{I_2}{I_1} \) is equal to ______.
\( 12 \)
\( 6 \)
\( 9 \)
\( 4 \)