1)(5х-3):2:(3-5х):7 2)(9у-2):5:(2-9у):3 3)(7-х):6:(х-7):9 4)(12-ав):5:(ав-12):6

$1)$ $(5x-3):2:(3-5x):7=\frac{5x-3}{2}:(3-5x)*\frac{1}{7}= \frac{\frac{5x-3}{2}}{3-5x}*\frac{1}{7}=\frac{5x-3}{2(3-5x)}*\frac{1}{7}=\frac{5x-3}{2(-(5x-3))}*\frac{1}{7}=\frac{1}{2*(-1)}*\frac{1}{7}=-\frac{1}{2}*\frac{1}{7}=- \frac{1}{14}$
$2)$ $(9y-2):5:(2-9y):3=\frac{9y-2}{5}:(2-9y)*\frac{1}{3}= \frac{\frac{9y-2}{5}}{2-9y}*\frac{1}{3}=\frac{9y-2}{5(2-9y)}*\frac{1}{3}=\frac{9y-2}{5(-(9y-2))}*\frac{1}{3}=\frac{1}{5*(-1)}*\frac{1}{3}=-\frac{1}{5}*\frac{1}{3}=- \frac{1}{15}$
$3$ $(7-x):6:(x-7):9= \frac{7-x}{6}:(x-7)*\frac{1}{9}=\frac{\frac{7-x}{6}}{x-7}*\frac{1}{9}=\frac{7-x}{6(x-7)}*\frac{1}{9}=$ $\frac{-(x-7)}{6(x-7)}*\frac{1}{9}=\frac{-1}{6}*\frac{1}{9}=-\frac{1}{54}$
$4)$ $(12-ab):5:(ab-12):6=\frac{12-ab}{5}:(ab-12)*\frac{1}{6}=\frac{\frac{12-ab}{5}}{ab-12}*\frac{1}{6}$ $\frac{12-ab}{5(ab-12)}*\frac{1}{6}=\frac{-(ab-12)}{5(ab-12)}*\frac{1}{6}=\frac{-1}{5}*\frac{1}{6}=-\frac{1}{30}$