Questions in differentiation

Select	Question
	If $x = a(t - \sin t)$and $y = a(1 - \cos t),$then $\frac{{dy}}{{dx}} = $
	If $x = \frac{{1 - {t^2}}}{{1 + {t^2}}}$and $y = \frac{{2at}}{{1 + {t^2}}}$, then $\frac{{dy}}{{dx}} = $
	If $x = a{\rm{ }}\left( {\cos t + \log \tan \frac{t}{2}} \right)\,,y = a\sin t,$then $\frac{{dy}}{{dx}} = $
	If $\tan y = \frac{{2t}}{{1 - {t^2}}}$and $\sin x = \frac{{2t}}{{1 + {t^2}}},$then $\frac{{dy}}{{dx}} = $
	If $x = \frac{{1 - {t^2}}}{{1 + {t^2}}}$and $y = \frac{{2t}}{{1 + {t^2}}}$, then $\frac{{dy}}{{dx}} = $
	If $x = a{t^2},y = 2at$, then $\frac{{{d^2}y}}{{d{x^2}}} = $
	If $\cos (x + y) = y\sin x,$then $\frac{{dy}}{{dx}} = $
	If $y = \frac{1}{4}{u^4},u = \frac{2}{3}{x^3} + 5$, then $\frac{{dy}}{{dx}} = $
	$x\sqrt {1 + y} + y\sqrt {1 + x} = 0$, then $\frac{{dy}}{{dx}} = $
	If $x = 2\cos t - \cos 2t$,$y = 2\sin t - \sin 2t$, then at $t = \frac{\pi }{4},\frac{{dy}}{{dx}} = $