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rút gọn P=2/x-(x2/(x2-xy)+(x2-y2)/xy-y2/(y2-xy)):(x2-xy+y2)/(x-y)
r tìm gt P với |2x-1|=1 ; |y+1|=1/2
![](https://rs.olm.vn/images/avt/0.png?1311)
\(a.2x\left(x-1\right)-3\left(x^2+4x\right)+x\left(x+2\right)\)
\(=2x^2-2x-3x^2-12x+x^2+2x\)
\(=-12x\)
\(b.\left(2x-3\right)\left(3x+5\right)-\left(x-1\right)\left(6x+2\right)+3-5x\)
\(=6x+10x-9x^2-15-6x^2-2x-6x-2+3-5x\)
\(=-15x^2+3x-14\)
\(c.\left(x-y\right)\left(x^2+xy+y^2\right)-\left(x+y\right)\left(x^2-y^2\right)\)
\(=x^3-y^3-x^3+y^3+x^2y-y^3\)
\(=y^3+x^2y\)
![](https://rs.olm.vn/images/avt/0.png?1311)
b: (x-y)(x^2-2x+y)
\(=x^3-2x^2+xy-x^2y+2xy-y^2\)
\(=x^3-2x^2-x^2y+3xy-y^2\)
c: \(\left(x^2-y\right)\left(x+y^2\right)-\left(x-y\right)\left(x^2+xy+y^2\right)\)
\(=x^3+x^2y^2-xy-y^3-\left(x^3-y^3\right)\)
\(=x^2y^2-xy\)
d: \(3x\left(2xy-z\right)-5y\left(x^2-2\right)+3xz\)
\(=6x^2y-3xz-5x^2y+10y+3xz\)
\(=x^2y+10y\)
![](https://rs.olm.vn/images/avt/0.png?1311)
1.
\(a,\left(-xy\right)\left(-2x^2y+3xy-7x\right)\)
\(=2x^3y^2-3x^2y^2+7x^2y\)
\(b,\left(\dfrac{1}{6}x^2y^2\right)\left(-0,3x^2y-0,4xy+1\right)\)
\(=-\dfrac{1}{20}x^4y^3-\dfrac{1}{15}x^3y^3+\dfrac{1}{6}x^2y^2\)
\(c,\left(x+y\right)\left(x^2+2xy+y^2\right)\)
\(=\left(x+y\right)^3\)
\(=x^3+3x^2y+3xy^2+y^3\)
\(d,\left(x-y\right)\left(x^2-2xy+y^2\right)\)
\(=\left(x-y\right)^3\)
\(=x^3-3x^2y+3xy^2-y^3\)
2.
\(a,\left(x-y\right)\left(x^2+xy+y^2\right)\)
\(=x^3-y^3\)
\(b,\left(x+y\right)\left(x^2-xy+y^2\right)\)
\(=x^3+y^3\)
\(c,\left(4x-1\right)\left(6y+1\right)-3x\left(8y+\dfrac{4}{3}\right)\)
\(=24xy+4x-6y-1-24xy-4x\)
\(=\left(24xy-24xy\right)+\left(4x-4x\right)-6y-1\)
\(=-6y-1\)
#Toru
![](https://rs.olm.vn/images/avt/0.png?1311)
a: Ta có: \(\left(x+y\right)^2\)
\(=x^2+2xy+y^2\)
\(\Leftrightarrow x^2+y^2=\dfrac{\left(x+y\right)^2}{2xy}\ge\dfrac{\left(x+y\right)^2}{2}\forall x,y>0\)
\(2\cdot\left(x^2+y^2\right)=\left(x+y\right)^2\)
\(2x^2+2y^2-\left(x^2+2xy+y^2\right)=0\)
\(2x^2+2y^2-x^2-2xy-y^2=0\)
\(x^2-2xy+y^2=0\)
\(\left(x-y\right)^2=0\)
\(x-y=0\)
vậy\(x=y\)