4xy -6x -2y + 3 bằng 13
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K
0
TQ
2
4 tháng 7 2023
`@` `\text {Ans}`
`\downarrow`
`A = `\(3x^2y-4xy+6x^2y+4xy \)
`= (3x^2y + 6x^2y) + (-4xy + 4xy)`
`= 9x^2y + 0`
`= 9x^2y`
`@` `\text {Kaizuu lv uuu}`
6 tháng 7 2016
\(=\frac{2x\left(x-2y\right)}{\left(x+2y\right)^2}:\frac{\left(2y-x\right)\left(2y+x\right)}{\left(x-2y\right)^2}:\frac{5xy\left(x-2y\right)}{\left(x+2y\right)^3}\)
Điều kiện: \(x\ne2y;x\ne-2y;x\ne0;y\ne0\)
\(=\frac{2x\left(x-2y\right)}{\left(x+2y\right)^2}:\frac{\left(2y+x\right)}{\left(x-2y\right)}:\frac{5xy\left(x-2y\right)}{\left(x+2y\right)^3}\)
\(=\frac{2x\left(x-2y\right)}{\left(x+2y\right)^2}\times\frac{x-2y}{x+2y}\times\frac{\left(x+2y\right)^3}{5xy\left(x-2y\right)}=\frac{2\left(x-2y\right)}{5y}\)
30 tháng 1 2022
\(=\dfrac{2x\left(x-2y\right)}{\left(x+2y\right)^2}\cdot\dfrac{\left(x-2y\right)^2}{-\left(x-2y\right)\left(x+2y\right)}:\dfrac{5x^2y-10xy^2}{x^3+6x^2y+12xy^3+8y^3}\)
\(=\dfrac{-2x\left(x-2y\right)^2}{\left(x+2y\right)^3}\cdot\dfrac{\left(x+2y\right)^3}{5xy\left(x-2y\right)}\)
\(=\dfrac{-2x\cdot\left(x-2y\right)}{5xy}=\dfrac{-2\left(x-2y\right)}{5y}\)
TN
0
K
1
22 tháng 10 2021
\(a,=\left(x-3\right)\left(6x^2y-4xy^2\right)=2xy\left(3x-2y\right)\left(x-3\right)\)
DH
16 tháng 8 2017
a, \(2x^2-4xy+4y^2-6x\)
\(=x^2-2xy-2xy+4y^2+x^2-3x-3x+9-9\)
\(=\left(x-2y\right)^2+\left(x-3\right)^2-9\)
Với mọi giá trị của \(x;y\in R\) ta có:
\(\left(x-2y\right)^2+\left(x-3\right)^2-9\ge-9\)
Để \(\left(x-2y\right)^2+\left(x-3\right)^2-9=-9\) thì
\(\left\{{}\begin{matrix}\left(x-2y\right)^2=0\\\left(x-3\right)^2=0\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}3-2y=0\\x=3\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}y=1,5\\x=3\end{matrix}\right.\)
Vậy..............
b, \(z^2-4zt+5t^2-2t+13\)
\(=z^2-2zt-2zt+4t^2+t^2-t-t+1+12\)
\(=\left(z-2t\right)^2+\left(t-1\right)^2+12\)
Với mọi giá trị của \(z;t\in R\) ta có:
\(\left(z-2t\right)^2+\left(t-1\right)^2+12\ge12\)
Để \(\left(z-2t\right)^2+\left(t-1\right)^2+12=12\) thì
\(\left\{{}\begin{matrix}\left(z-2t\right)^2=0\\\left(t-1\right)^2=0\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}z-2=0\\t=1\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}z=2\\t=1\end{matrix}\right.\)
Vậy...............
Câu c tường tự !!!
TN
16 tháng 8 2017
a,Đặt A= \(2x^2-4xy+4y^2-6x\)
\(=\left(2x^2-4xy-6x\right)+4y^2\)
\(=2\left(x^2-2xy-3x\right)+4y^2\)
\(=2\left[x^2-2x\left(y+\dfrac{3}{2}\right)+\left(y+\dfrac{3}{2}\right)^2\right]+4y^2-\left(y+\dfrac{3}{2}\right)^2\)
\(=2\left(x-y-\dfrac{3}{2}\right)^2+4y^2-y^2-3y-\dfrac{9}{4}\)
\(=2\left(x-y-\dfrac{3}{2}\right)^2+3\left(y^2-y+\dfrac{1}{4}\right)-3\)
\(=2\left(x-y-\dfrac{3}{2}\right)^2+3\left(y-\dfrac{1}{2}\right)^2-3\)
Với mọi giá trị của x;y ta có:
\(\left(x-y-\dfrac{3}{2}\right)^2\ge0;\left(y-\dfrac{1}{2}\right)^2\ge0\)
\(\Rightarrow2\left(x-y-\dfrac{3}{2}\right)^2+\left(y-\dfrac{1}{2}\right)^2-3\ge-3\)
Vậy Min A = -3 khi \(\left\{{}\begin{matrix}x-y-\dfrac{3}{2}=0\\y-\dfrac{1}{2}=0\end{matrix}\right.\)
\(\Rightarrow\left\{{}\begin{matrix}x-\dfrac{1}{2}-\dfrac{3}{2}=0\\y=\dfrac{1}{2}\end{matrix}\right.\)
\(\Rightarrow\left\{{}\begin{matrix}x-2=0\\y=\dfrac{1}{2}\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=2\\y=\dfrac{1}{2}\end{matrix}\right.\)
b, Đặt B = \(z^2-4zt+5t^2-2t+13\)
\(=\left(z^2-4zt+4t^2\right)+\left(t^2-2t+1\right)+12\)
\(=\left(z-2t\right)^2+\left(t-1\right)^2+12\)
Với mọi giá trị của z;t ta có:
\(\left(z-2t\right)^2\ge0;\left(t-1\right)^2\ge0\)
\(\Rightarrow\left(z-2t\right)^2+\left(t-1\right)^2+12\ge12\)
Vậy Min B = 12 khi \(\left\{{}\begin{matrix}z-2t=0\\t-1=0\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}z-2=0\\t=1\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}z=2\\t=1\end{matrix}\right.\)
c, Đặt C = \(16x^2-8x+y^2-2y\)
\(=\left(16x^2-8x+1\right)+\left(y^2-2y+1\right)-2\)
\(=\left(4x-1\right)^2+\left(y-1\right)^2-2\)
Với mọi giá trị x;y ta có:
\(\left(4x-1\right)^2\ge0;\left(y-1\right)^2\ge0\)
\(\Rightarrow\left(4x-1\right)^2+\left(y-1\right)^2-2\ge-2\)
Vậy Min C = -2 khi \(\left\{{}\begin{matrix}4x-1=0\\y-1=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}4x=1\\y=1\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=\dfrac{1}{4}\\y=1\end{matrix}\right.\)
\(\left(4xy-2y\right)-\left(6x-3\right)=13\)
\(\Leftrightarrow2y\left(2x-1\right)-3\left(2x-1\right)=13\)
\(\Leftrightarrow\left(2x-1\right)\left(2y-3\right)=13=1.13\)
\(\Rightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}2x-1=1\\2y-3=13\end{matrix}\right.\\\left\{{}\begin{matrix}2x-1=13\\2y-3=1\end{matrix}\right.\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x=1\\y=8\end{matrix}\right.\\\left\{{}\begin{matrix}x=7\\y=2\end{matrix}\right.\end{matrix}\right.\)