If $x = \cos\: t ( 3-2 \: \cos^2 t)\: and \: y = \sin \: t ( 3-2 \sin^2\: t)$ find the value of $\large\frac{dy}{dx}$ at $t = \large\frac{\pi}{4}$

Question

$(a)\; sint\qquad(b)\; 3cost-sint\qquad(c)\; sin2t .sint\qquad(d)\; 3cost-3sin2t .sint$