tìm x,y và z biết x^2-2xy+y^2+4y+5+(2z-3)^2=0
Tìm x,y,z biết: a) x^2+y^2-4x+4y+8=0 b) 5x^2-4xy+y^2=0 c) x^2+2y^2+z^2-2xy-2y-4z+5=0 d) 3x^2+3y^2+3xy-3x+3y+3=0 e) 2x^2+y^2+2z^2-2xy-2xz+2yz-2z-2z-2x+2=0
a) x2+y2-4x+4y+8=0
⇔ (x-2)2+(y+2)2=0
\(\Leftrightarrow\left\{{}\begin{matrix}x-2=0\\y+2=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=2\\y=-2\end{matrix}\right.\)
b)5x2-4xy+y2=0
⇔ x2+(2x-y)2=0
\(\Leftrightarrow\left\{{}\begin{matrix}x=0\\2x-y=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=0\\y=0\end{matrix}\right.\)
c)x2+2y2+z2-2xy-2y-4z+5=0
⇔ (x-y)2+(y-1)2+(z-2)2=0
\(\Leftrightarrow\left\{{}\begin{matrix}x-y=0\\y-1=0\\z-2=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=y=1\\z=2\end{matrix}\right.\)
b: Ta có: \(5x^2-4xy+y^2=0\)
\(\Leftrightarrow x^2-\dfrac{4}{5}xy+y^2=0\)
\(\Leftrightarrow x^2-2\cdot x\cdot\dfrac{2}{5}y+\dfrac{4}{25}y^2+\dfrac{21}{25}y^2=0\)
\(\Leftrightarrow\left(x-\dfrac{2}{5}y\right)^2+\dfrac{21}{25}y^2=0\)
Dấu '=' xảy ra khi \(\left\{{}\begin{matrix}x=0\\y=0\end{matrix}\right.\)
d)3x2+3y2+3xy-3x+3y+3=0
⇔ 6x2+6y2+6xy-6x+6y+6=0
⇔ 3(x+y)2+3(x-1)2+3(y+1)2=0
\(\Leftrightarrow\left\{{}\begin{matrix}x+y=0\\x-1=0\\y+1=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=1\\y=-1\end{matrix}\right.\)
tìm x,y,z biết \(x^2-2xy+y^2+4y+5+\left(2z-3\right)^2=0\)
Tìm x, y và z biết: \(x^2-2x+y^2+4y+5+\left(2z-3\right)^2=0\)
Lời giải:
$x^2-2x+y^2+4y+5+(2z-3)^2=0$
$\Leftrightarrow (x^2-2x+1)+(y^2+4y+4)+(2z-3)^2=0$
$\Leftrightarrow (x-1)^2+(y+2)^2+(2z-3)^2=0$
Vì $(x-1)^2\geq 0; (y+2)^2\geq 0; (2z-3)^2\geq 0$ với mọi $x,y,z$
Do đó để tổng của chúng bằng $0$ thì $(x-1)^2=(y+2)^2=(2z-3)^2=0$
$\Leftrightarrow x=1; y=-2; z=\frac{3}{2}$
Tìm x;y;z biết: x2-2xy+2y2+4y+4+(2z-3)2=0
x2-2xy+2y2+4y+4+(2z-3)2=0
(x2-2xy+y2)+(y2+4y+4)+(2z-3)2=0
(x-y)2+(y+2)2+(2z-3)2=0
=>x-y=y+2=2z-3=0
=>z=3/2
y=-2
x=-2
tìm x,y,z biết
x^2-2x+y^2+4y+5+(2z-3)^2=0
\(x^2-2x+y^2+4y+5+\left(2z-3\right)^2=0\)
\(\Leftrightarrow\left(x^2-2x+1\right)+\left(y^2+4y+4\right)+\left(2z-3\right)^2=0\)
\(\Leftrightarrow\left(x-1\right)^2+\left(y+2\right)^2+\left(2z-3\right)^2=0\)
Vì \(\hept{\begin{cases}\left(x-1\right)^2\ge0\\\left(y+2\right)^2\ge0\\\left(2z-3\right)^2\ge0\end{cases}}\) nên \(\left(x-1\right)^2+\left(y+2\right)^2+\left(2z-3\right)^2\ge0\)
Dấu "=" xảy ra \(\Leftrightarrow\hept{\begin{cases}\left(x-1\right)^2=0\\\left(y-2\right)^2=0\\\left(2z-3\right)^2=0\end{cases}\Rightarrow\hept{\begin{cases}x=1\\y=2\\z=\frac{3}{2}\end{cases}}}\)
cho x^2-2x+y^2+4y+5+(2z-3)^2=0 tìm x;y;z
1/tính giá trị x+y biết x-3/y-5=3/5 và y-x=4
2/tìm x biết 15-x/7=x+7/4
3/tìm x,y,z biết 4/3x-2y=3/2z-4x=2/4y-3z và x+y-z=-10
4/tìm x,y,z biết x-1/2=y+3/4=z-5/6 và 5z-3x-4y=50
mấy bạn giúp mình nha mình cần gấp khoảng 1 giờ đã nộp bài gồi
Cho x;y;z khác 0 và 3x-2y/2015=2z-4x/2016=4y-3z/2017
Tính P = x^2-2xy-z^2/x^2+y^2+z^2
\(\frac{3x-2y}{2015}=\frac{2x-4x}{2016}=\frac{4y-3z}{2017}\)
\(\Rightarrow\frac{12x-8y}{8060}=\frac{6z-12x}{6048}=\frac{8y-6z}{4034}=\frac{\left(12x-8y\right)+\left(6z-12x\right)+\left(8y-6z\right)}{8060+6048+4034}=0\)
\(\Leftrightarrow\hept{\begin{cases}3x-2y=0\\2z-4x=0\\4y-3z=0\end{cases}\Leftrightarrow\hept{\begin{cases}3x=2y\\2z=4x\\4y=3z\end{cases}}}\Leftrightarrow\hept{\begin{cases}\frac{x}{2}=\frac{y}{3}\\\frac{x}{2}=\frac{z}{4}\\\frac{y}{3}=\frac{z}{4}\end{cases}}\)
\(\Rightarrow\frac{x}{2}=\frac{y}{3}=\frac{z}{4}=k\left(k\ne0\right)\)
\(\Rightarrow x=2k;y=3k;z=4k\)
Thay vào P ta có
\(P=\frac{4k^2-2.2k.3k-16k^2}{4k^2+9k^2+16k^2}=\frac{k^2\left(4-12-16\right)}{k^2\left(4+9+16\right)}=-\frac{24}{29}\)
Tìm x,y:
a, 2x2+ y2+ 2xy-10x -4y+13=0
b, x2+ y2+z2 -4x+6y -2z+14=0
c, 2x2+ y2+ 2z2 + 2xy + 2xz + 2yz + 2x - 4z+ 5=0
a) \(\Leftrightarrow4x^2+2y^2+4xy-20x-8y+26=0\)
\(\Leftrightarrow4x^2+4x\left(y-5\right)+\left(y-5\right)^2-\left(y-5\right)^2+2y^2-8y+26=0\)
\(\Leftrightarrow\left(2x+y-5\right)^2+y^2+2y+1=0\)
\(\Leftrightarrow\left(2x+y-5\right)^2+\left(y+1\right)^2=0\)
\(\Leftrightarrow\left\{{}\begin{matrix}2x+y-5=0\\y+1=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=3\\y=-1\end{matrix}\right.\) ( TM )
b) \(\Leftrightarrow\left(x^2-4x+4\right)+\left(y^2+6y+9\right)+\left(z^2-2z+1\right)=0\)
\(\Leftrightarrow\left(x-2\right)^2+\left(y+3\right)^2+\left(z-1\right)^2=0\)
\(\Leftrightarrow\left\{{}\begin{matrix}x-2=0\\y+3=0\\z-1=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=2\\y=-3\\z=1\end{matrix}\right.\) ( TM )
c) \(\Leftrightarrow\left(x^2+y^2+z^2+2xy+2yz+2xz\right)+\left(x^2+2x+1\right)+\left(z^2-4z+4\right)=0\)
\(\Leftrightarrow\left(x+y+z\right)^2+\left(x+1\right)^2+\left(z-2\right)^2=0\)
\(\Leftrightarrow\left\{{}\begin{matrix}x+y+z=0\\x+1=0\\z-2=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=-1\\y=-1\\z=2\end{matrix}\right.\) ( TM )