Ta có:-2/4=x/10=>4.x=-2.10=>4.x=-20=>x=-20:4=>x=-5
Thay x=-5 ta có:-5/10=-7/y=>10.(-7)=y.(-5)=>y.(-5)=-70=>y=-70:(-5)=>y=14
Thay y=14 ta có:-7/14=z/-24=>14.z=-24.(-7)=>14.z=168=>z=168:14=>z=12
Vậy x=-5;y=14;z=12
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$M=(\frac{1}{x+1}+\frac{2}{1-x}+\frac{x}{x^2-1})\div \frac{1}{x+1}\\=-\frac{3}{(x-1)(x+1)}\times (x+1)\\=-\ ...