Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.
![](https://rs.olm.vn/images/avt/0.png?1311)
Học tốt nha bn ! ( dòng * ko cần ghi vào đâu bn đây là nháp giở của mik )
![](https://rs.olm.vn/images/avt/0.png?1311)
a) 5x2 + 10y2 - 6xy - 4x - 2y + 3
= ( x2 - 6xy + 9y2 ) + ( 4x2 - 4x + 1 ) + ( y2 - 2y + 1 ) + 1
= ( x - 3y )2 + ( 2x - 1 )2 + ( y - 1 )2 + 1
Ta có : \(\hept{\begin{cases}\left(x-3y\right)^2\\\left(2x-1\right)^2\\\left(y-1\right)^2\end{cases}}\ge0\forall x,y\Rightarrow\left(x-3y\right)^2+\left(2x-1\right)^2+\left(y-1\right)^2+1\ge1>0\forall x,y\)
=> đpcm
b) x2 + 4y2 + z2 - 2x - 6z + 8y + 15 = 0 < Sửa -z2 -> +z2 )
= ( x2 - 2x + 1 ) + ( 4y2 + 8y + 4 ) + ( z2 - 6z + 9 ) + 1
= ( x - 1 )2 + 4( y2 + 2y + 1 ) + ( z - 3 )2 + 1
= ( x - 1 )2 + 4( y + 1 )2 + ( z - 3 )2 + 1
Ta có : \(\hept{\begin{cases}\left(x-1\right)^2\ge0\forall x\\4\left(y+1\right)^2\ge0\forall y\\\left(z-3\right)^2\ge0\forall z\end{cases}}\Rightarrow\left(x-1\right)^2+4\left(y+1\right)^2+\left(z-3\right)^2+1\ge1>0\forall x,y,z\)
=> đpcm
![](https://rs.olm.vn/images/avt/0.png?1311)
a/ \(x^2+xy+y^2+1=\left(x^2+xy+\frac{y^2}{4}\right)+\frac{3}{4}y^2+1=\left(x+\frac{y}{2}\right)^2+\frac{3y^2}{4}+1\ge1>0\)
với mọi x,y
b/ \(x^2+5y^2+2x-4xy-16y+14=x^2-2x\left(2y-1\right)+\left(4y^2-4y+1\right)+\left(y^2-12y+36\right)-23\)
\(=\left(x-2y+1\right)^2+\left(y-6\right)^2-23\ge-23\)
Bạn xem lại đề
2 câu trên đã có kết quả, mình giải quyết câu c nhá
5x2 + 10y2 - 6xy - 4x - 2y + 3 > 0
5x2 + 10y2 - 6xy - 4x - 2y + 3 = x2 + 4x2 + y2 + 9y2 - 6xy - 4x - 2y + 3
=[(2x)2 - 2*2x + 1] + (y2 - 2y + 1) + [(3y)2 - 2*3y + x2 ] + 1
=(2x + 1)2 + (y - 1)2 + (3y - x)2 + 1
(2x + 1)2 \(\ge\)0 với mọi x
(y - 1)2 \(\ge\) 0 với mọi y
(3y - x)2\(\ge\) 0 với mọi x và y
1>0
=> ĐPCM
![](https://rs.olm.vn/images/avt/0.png?1311)
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 \(\left\{{}\begin{matrix}x=0\\y=0\end{matrix}\right.\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a)\(x^2+2y^2+2xy-2y+1=0\)
\(\Leftrightarrow x^2+2xy+y^2+y^2-2y+1=0\)
\(\Leftrightarrow\left(x+y\right)^2+\left(y-1\right)^2=0\)
\(\Leftrightarrow\hept{\begin{cases}y-1=0\\x+y=0\end{cases}}\Leftrightarrow\hept{\begin{cases}y=1\\x=-y=-1\end{cases}}\)
Vậy x=-1 y=1
a) \(x^2+2y^2+2xy-2y+1=0\)
\(\Leftrightarrow\left(x^2+2xy+y^2\right)+\left(y^2-2y+1\right)=0\)
\(\Leftrightarrow\left(x+y\right)^2+\left(y-1\right)^2=0\)
\(\Rightarrow\orbr{\begin{cases}\left(x+y\right)^2=0\\\left(y-1\right)^2=0\end{cases}}\Leftrightarrow\orbr{\begin{cases}x+y=0\\y-1=0\end{cases}\Leftrightarrow\orbr{\begin{cases}x=-y\\y=1\end{cases}\Rightarrow}x=-1;y=1}\)
b) \(5x^2+3y^2+z^2-4x+6xy+4z+6=0\)
\(\Leftrightarrow\left(2x^2-4x+2\right)+\left(3x^2+6xy+3y^2\right)+\left(z^2+4z+4\right)=0\)
\(\Leftrightarrow2.\left(x-1\right)^2+3.\left(x+y\right)^2+\left(z+2\right)^2=0\)
\(\Rightarrow\) \(\left(x-1\right)^2=0\Rightarrow x-1=0\Rightarrow x=1\)
\(\left(x+y\right)^2=0\Rightarrow x+y=0\Rightarrow y=-x=-1\)
\(\left(z+2\right)^2=0\Rightarrow z+2=0\Rightarrow z=-2\)