giải phương trình a) 7/x+2+2/x+3=1/x ²+5x+6 b)4/x-2+x/x+1=x ²-2/x ²-x-2 c)x/x+2-x ²+1/x ²-2x-8=3/x-4 d) x/2x+1-2/x-3=x ²+5/2x ²-5x-3

`a)`

 `7/(x+2)+2/(x+3)=1/(x²+5x+6)`     `(`ĐKXĐ `x\ne -2` ;`x \ne -3“)`

`⇔  (7(x+3)+2(x+2))/((x+2).(x+3))=1/((x+2)(x+3))`

`⇒ 7x + 21+2x+4=1`

`⇔ 9x +25 =1`

`⇔ 9x=-24`

`⇔ x= (-8)/3` `(TMĐK)`

`b)`

`4/(x-2)+x/(x+1)=(x²-2)/(x²-x-2)`    `(`ĐKXĐ `x\ne -1` ;`x \ne 2“)`

`⇔(4(x+1)+x(x-2))/((x-2)(x+1))=(x²-2)/((x+1)(x-2))`

`⇒ 4x +4 + x² -2x=x²-2`

`⇔ 2x + x² -x² =-2-4`

`⇔ 2x = -6`

`⇔ x=-3`  `(TMĐK)`

`c)`

`x/(x+2)-(x²+1)/(x²-2x-8)=3/(x-4)`    `(`ĐKXĐ `x\ne -2` ;`x \ne 4“)`

`⇔x/(x+2)-(x²+1)/(x²-2x-8)-3/(x-4)=0`

`⇔ (x(x-4)-(x²+1)-3(x+2))/((x+2).(x-4))=0`

`⇒ x² -4x-x²-1 -3x -6=0`

`⇔ -7x -7=0`

`⇔ -7x=7`

`⇔ x=-1` `(TMĐK)`

`d)`

 `x/(2x+1)-2/(x-3)=(x²+5)/(2x ²-5x-3)`    `(`ĐKXĐ `x\ne -0,5` ;`x \ne 3“)`

`⇔ (x(x-3)-2(2x+1))/((2x+1).(x-3))=(x²+5)/((2x+1).(x-3)` 

`⇒ x² -3x-4x -2=x²+5`

`⇔ x² -x² -7x=5 +2`

`⇔ -7x=7`

`⇔ x=-1`  `(TMĐK)`