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![](https://rs.olm.vn/images/avt/0.png?1311)
a: \(=-\left(10x^2+15x-8x-12\right)=-10x^2-7x+12\)
![](https://rs.olm.vn/images/avt/0.png?1311)
1: ĐKXĐ: \(x\notin\left\{0;3\right\}\)
\(\dfrac{x+3}{x}-\dfrac{x}{x-3}+\dfrac{9}{x^2-3x}\)
\(=\dfrac{x+3}{x}-\dfrac{x}{x-3}+\dfrac{9}{x\left(x-3\right)}\)
\(=\dfrac{\left(x+3\right)\left(x-3\right)-x^2+9}{x\left(x-3\right)}\)
\(=\dfrac{x^2-9-x^2+9}{x\left(x-3\right)}\)
=0
2: ĐKXĐ: \(x\notin\left\{0;1\right\}\)
\(\dfrac{3}{x}-\dfrac{5}{x-1}+\dfrac{3x+2}{x^2-x}\)
\(=\dfrac{3}{x}-\dfrac{5}{x-1}+\dfrac{3x+2}{x\left(x-1\right)}\)
\(=\dfrac{3x-3-5x+3x+2}{x\left(x-1\right)}\)
\(=\dfrac{x-1}{x\left(x-1\right)}=\dfrac{1}{x}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
mình làm bài 2 trước nha:
a) y.(a-b)+a.(y-b)=a.y-b.y+a.y-b.y
=(a.y+a.y)-(b.y+b.y)
=2.a.y-2.b.y
=2.y.(a-b)
b)x2.(x+y)-y.(x2-y2)=x3+x2.y-x2y+y3=x3+y3
![](https://rs.olm.vn/images/avt/0.png?1311)
b: \(=\dfrac{x+5+x+x-5}{x\left(x+5\right)}=\dfrac{3x}{x\left(x+5\right)}=\dfrac{3}{x+5}\)
\(a,=-3x^3+x^2+9x^2-3x-12x+4=-3x^3+10x^2-15x+4\\ b,=\dfrac{x+5+x+x-5}{x\left(x+5\right)}=\dfrac{3x}{x\left(x+5\right)}=\dfrac{3}{x+5}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
Bài 1 :
\(\frac{x^3-9x}{15-5x}=\frac{-x^2-3x}{5}\left(ĐKXĐ:x\ne3\right)\)
\(\Leftrightarrow5\left(x^3-9x\right)=-\left(x^2+3x\right)\left(15-5x\right)\)
\(\Leftrightarrow5x^3-45x=5x^3-45\) ( luôn đúng )
Do đó : \(\frac{x^3-9x}{15-5x}=\frac{-x^2-3x}{5}\left(x\ne3\right)\)
P/s : Bài này thì xét tích chéo của hai số thôi nhé @
1. 2x2y(2x2+3x+3)
= 4x4y +6x3y+6x2y
2) ( 4x2y + 6xy2 - 2x )1/2xy2
= 2x3y3 +3x2y4-x2y2