ĐKXĐ: `x>=0;x\ne9`

`(x^2-3)/(sqrtx-3)=((x-sqrt3)(x+sqrt3))/(x+sqrt3)=x-sqrt3`

`a)(x^2-3)/(x+\sqrt3)`

`->` ĐKXĐ : `x>=0;x\ne9`

`=((x-\sqrt3)(x+\sqrt3))/(x+\sqrt3)`

`=(x-\sqrt3)/1`

`=x-\sqrt3`

Khi x=2 thì A=4+2+12=18

Ta có:

\(\dfrac{x-\sqrt{x}}{\sqrt{x}-1}-\dfrac{x-1}{\sqrt{x}+1}\);\(ĐK:x\ge0;x\ne1\)

\(\Leftrightarrow\dfrac{\sqrt{x}\left(\sqrt{x}-1\right)}{\sqrt{x}-1}-\dfrac{\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}{\sqrt{x}+1}\)

\(\Leftrightarrow\sqrt{x}-\left(\sqrt{x}-1\right)\)

\(\Leftrightarrow\sqrt{x}-\sqrt{x}+1\)

\(\Leftrightarrow1\)

a: \(=\sqrt{x}\cdot\dfrac{\left(\sqrt{x}-1\right)}{\sqrt{x}-1}-\dfrac{\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}{\sqrt{x}+1}\)

\(=\sqrt{x}-\sqrt{x}+1=1\)

`Answer:`

`a)`

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

`=>A=5(x^2+2x+1)-3(x^2-6x+9)-4x^2+16`

`=>A=5x^2+10x+5-3x^2+18x-27-4x^2+16`

`=>A=(5x^2-3x^2-4x^2)+(10x+18x)+(5-27+16)`

`=>A=-2x^2+28x-6`

`b)`

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

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

`=6x^2+10x-9x-15-2x^3+8x^2-8x-4x^2+9`

`=(6x^2-4x^2+8x^2)-2x^3+(10x-9x-8x)+(-15+9)`

Thay `x=-7` vào ta được:

`B=10(-7)^2-2(-7)^3-7(-7)-6`

`=>B=10.49-2(-343)+49-6`

`=>B=490+686+49-6`

`=>B=1219`

a, ( x+ 2 )( x - 2 ) - ( x-3 ( x-1)

= \(^{x^2}\) - \(2^2\) - ( \(x^2\)+ x - 3x - x)

= \(x^2\) - 4 - \(x^2\) - x  + 3x  + 3

= 2x -1

a) \(\left(x+2\right)\left(x-2\right)-\left(x-3\right)\left(x+1\right)\)

\(=x^2-2^2-\left(x^2+x-3x-x\right)\)

\(=x^2-4-x^2-x+3x+3\)

\(=2x-1\)

Bạn Trần Huyền Trang làm sai rồi.

a) \(\sqrt[]{1-4a+4a^2}\)

\(=\sqrt[]{\left(1-2a\right)^2}\)

\(=\left|1-2a\right|\)

\(=\left[{}\begin{matrix}1-2a\left(a\le\dfrac{1}{2}\right)\\2a-1\left(a>\dfrac{1}{2}\right)\end{matrix}\right.\)

b) \(x-2y-\sqrt[]{x^2-4xy+4y^2}\)

\(=x-2y-\sqrt[]{\left(x-2y\right)^2}\)

\(=x-2y-\left|x-2y\right|\)

\(=\left[{}\begin{matrix}x-2y-x+2y\left(x\ge2y\right)\\x-2y+x-2y\left(x< 2y\right)\end{matrix}\right.\)

\(=\left[{}\begin{matrix}0\left(x\ge2y\right)\\2x-4y\left(x< 2y\right)\end{matrix}\right.\)

\(=\left[{}\begin{matrix}0\left(x\ge2y\right)\\2\left(x-2y\right)\left(x< 2y\right)\end{matrix}\right.\)

chịu

Lời giải:

ĐKXĐ: $x\geq 0$

$=\frac{(\sqrt{x}-2)(\sqrt{x}+2)+10-x}{\sqrt{x}+2}=\frac{x-4+10-x}{\sqrt{x}+2}=\frac{6}{\sqrt{x}+2}$