Cách làm cho bạn:
a) $\frac{3}{4}+\frac{1}{9}$:x=0,5 => $\frac{1}{9}:x=\frac{1}{2}−\frac{3}{4}$ nên x=$\frac{1}{9}/(\frac{−1}{4})=\frac{−4}{9}$
b) $\frac{3}{4}−(x−\frac{2}{3})=1\frac{1}{3}$ => x=$\frac{2}{3}−\frac{4}{3}+\frac{3}{4}=\frac{1}{12}$
c) $(\frac{5}{7}−x).\frac{11}{15}=\frac{−22}{45}$ =>$\frac{5}{7}−x=(\frac{−22}{45}):\frac{11}{15}$ nên x=$\frac{29}{21}$
d) (2,5x−$\frac{4}{7}):\frac{8}{21}$=−1,5 => 2,5x−$\frac{4}{7}=(\frac{−3}{2}).\frac{8}{21}$ nên x = 0
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