Đáp án:
`a) 3x=5y;4y=6z`
`<=> x/5=y/3;y/6=z/4`
`<=> x/10=y/6=z/4=(2y)/12`
áp dụng tính chất tỉ số bằng nhau ta có:
`x/10=(2y)/12=z/4=(x-2y+z)/(10-12+4)=40/2=20`
`<=>x=20.10=200; y=20.6=120; z=20.4=80`
`c) -4x=3y; 5y=-10z`
`<=> x/3=y/(-4);y/(-10)=z/5`
`<=> x/15=y/(-20)=z/10=(x+y+z)/(15-20+10)=35/5=7`
`<=> x=7.15=105; y=7.(-20)=-140; z=7.10=70`
`d) x/11=y/10; y/12=z/7`
`<=> x/66=y/60=z/35=(3z)/105=(x+y-3z)/(66+60-105)=84/21=4`
`<=> x=4.66=264; y=4.60=240; z=4.35=140`