`#AkaShi`
`A=2x+xy²-x²y-2y`
`A=(2x-x²y)+(xy²-2y)`
`A=x(2-xy)+y(xy-2)`
`A=x(2-xy)-y(2-xy)`
`A=(2-xy)(x-y)`
Thay `x=-1/2;y=-1/3`
`[2-(-1/2)xx(-1/3)][-1/2-(-1/3)]=11/6xx-1/6=-11/36`
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`x(x-5)+4x+20=0`
`⇔x(x-5)+4(x-5)=0`
`⇔(x-5)(x+4)=0`
`1) x-5=0⇔x=5`
`2) x+4=0⇔x=-4`
Vậy `S={5;-4}`
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`x(x+6)-7x-42=0`
`⇔x(x+6)-7(x+6)=0`
`⇔(x+6)(x-7)=0`
`1) x+6=0⇔x=-6`
`2) x-7=0⇔x=7`
Vậy `S={-6;7}`
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`x³-5x²+x-5=0`
`⇔x²(x-5)+(x-5)=0`
`⇔(x-5)(x²+1)=0`
`1) x-5=0⇔x=5`
`2) x²+1=0⇔x^2=-1` (vô nghiệm)
Vậy `S={5}`
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`x^4-2x³+10x²-20x=0`
`⇔x³(x-2)+10x(x-2)=0`
`⇔(x-2)(x²+10x)=0`
`⇔x(x-2)(x+10)=0`
`1) x=0`
`2) x-2=0⇔x=2`
`3) x+10=0⇔x=-10`
Vậy `S={-10;0;2}`
