`#DyHungg`
`a) 7-3x=9-x`
`⇔-3x+x=9-7`
`⇔-2x=2`
`⇔x=-1`
Vậy S={-1}`
..................
`b) (x+2)(x²-3x+5)=(x+2)x²`
`⇔(x+2)(x²-3x+5)-(x+2)x²=0`
`⇔(x+2)(x²-x²-3x+5)=0`
`⇔(x+2)(-3x+5)=0`
`1) x+2=0⇔x=-2`
`2) -3x+5=0⇔x=5/3`
Vậy `S={-2;5/3}`
...............
`c) 2/(x+1)-1/(x-2)=(3x-11)/((x+1)(x-2))`
`ĐKXĐ: x` $\neq$ `-1;2`
`⇔(2(x-2))/((x+1)(x-2))-(x+1)/((x+1)(x-2))=(3x-11)/((x+1)(x-2))`
`⇒2x-2-x-1=3x-11`
`⇔2x-3x-x=-11+1+2`
`⇔-2x=-8`
`⇔x=4 (TM)`
Vậy `S={4}`
