1 . Thực hiện phép tính

Đáp án:

 `a)`

`x.(3-x)+(2x^{3}-8x^{2}):2x` `(x\ne0)`

`=3x-x^{2}+x^{2}-4x`

`=(x^{2}-x^{2})+(3x-4x)`

`=-x`

`b)`

`\frac{x+1}{2x+6}:\frac{2x+3}{x^{2}+3x}` `(x\ne0;x\ne-3;x\ne-\frac{3}{2};x\ne-1)`

`=\frac{x+1}{2.(x+3)}.\frac{x.(x+3)}{2x+3}`

`=\frac{(x+1).x.(x+3)}{2.(x+3).(2x+3)}`

`=\frac{x.(x+1)}{2.(2x+3)}`

`c)`

`\frac{x^{2}-25}{x}:\frac{x^{2}-10x+25}{x}` `(đk: x\ne0;x\ne5;x\ne-5)`

`=\frac{x^{2}-5^{2}}{x}.\frac{x}{x^{2}-2.x.5+5^{2}}`

`=\frac{(x-5).(x+5).x}{x.(x-5)^{2}}`

`=\frac{(x-5).(x+5)}{(x-5)^{2}}`

`=\frac{x+5}{x-5}`