tìm x biết 1) (x+2)^2+(x-3)^2-2(x-1)(x+1)=9 2) (x+2)(x^2-2x+4)-(x^3+2x^2)=5 rút gọn biểu thức sau :1) (2x+5)(x-2)-3(x+2)^2+(x+1)^2

Tìm `x`:

`1)(x+2)^2+(x-3)^2-2(x-1)(x+1)=9`

`⇔x^2+4x+4+x^2-6x+9-2x^2+2=9`

`⇔-2x+15=9`

`⇔-2x=-6`

`⇔x=3`

Vậy `S={3}`

`2)(x+2)(x^2-2x+4)-(x^3+2x^2)=5`

`⇔x^3-2x^2+4x+2x^2-4x+8-x^3-2x^2=5`

`⇔-2x^2+8=5`

`⇔-2x^2=-3`

`⇔x^2=3/2`

`⇔x^2=“(`$\sqrt[]{\dfrac{3}{2}}$ `)^2` 

`⇔x=+-`$\sqrt[]{\dfrac{3}{2} }$

Vậy `S={+-`$\sqrt[]{\dfrac{3}{2} }$`}`

Rút gọn biểu thức:

`1)(2x+5)(x-2)-3(x+2)^2+(x+1)^2`

`=2x^2-4x+5x-10-3(x^2+4x+4)+(x^2+2x+1)`

`=2x^2+x-10-3x^2-12x-12+x^2+2x+1`

`=(2x^2-3x^2+x^2)+(x-12x+2x)+(-10-12+1)`

`=-9x-21`

`2)(x+3)(x-3)-(x+5)(x-1)-(x-4)^2`

`=x^2-9-x^2+x-5x+5-x^2+8x-16`

`=(x^2-x^2-x^2)+(x-5x+8x)+(-9+5-16)`

`=-x^2+4x-20`