Ta có : 

      x - y - z = 0

=> 

Có : 

   \(B=\left(1-\frac{z}{x}\right).\left(1-\frac{x}{y}\right).\left(1+\frac{y}{z}\right)\)

  \(B=\left(\frac{x-z}{x}\right).\left(\frac{y-x}{y}\right).\left(\frac{z+y}{z}\right)\)

Thay các biểu thức trong khung trên và B ta có :

 \(B=\frac{y}{x}.\frac{y-\left(y+z\right)}{y}.\frac{x}{z}\)

=> \(B=\frac{y}{x}.\frac{y-y-z}{y}.\frac{x}{z}=\frac{y.\left(-z\right).x}{x.y.z}=-1\)

Vậy B = -1

nha !!!

Ta có: \(x-y-z=0\Rightarrow\hept{\begin{cases}x=z+y\\y=x-z\\-z=y-x\end{cases}}\)

\(B=\left(1-\frac{z}{x}\right).\left(1-\frac{x}{y}\right).\left(1+\frac{y}{z}\right)\)

\(\Rightarrow B=\frac{x-z}{x}.\frac{y-x}{y}.\frac{z+y}{z}\)

\(\Rightarrow B=\frac{y}{x}.\frac{-z}{y}.\frac{x}{z}\)

\(\Rightarrow B=\frac{y.\left(-z\right).x}{x.y.z}=-1\)

Vậy giá trị của biểu thức \(B=-1.\)

Ta có :\(x+y+z=0\Rightarrow\left(x+y+z\right)^2=x^2+y^2+z^2+2xy+2yz+2xz=0\)

\(\Leftrightarrow x^2+y^2+z^2+2\left(xy+yz+xz\right)=x^2+y^2+z^2=0\) (do xy + yz + xz = 0)

Ta lại thấy \(x^2;y^2;z^2\ge0\forall x;y;z\) nên \(x^2+y^2+z^2\ge0\forall x;y;z\)

Dấu "=" xảy ra \(\Leftrightarrow x=y=z=0\) thay vào S ta được :

\(S=\left(-1\right)^{2005}+\left(-1\right)^{2006}+1^{2007}=1\)

\(x^3+y^3+z^3=3xyz\)

\(\Rightarrow x^3+y^3+z^3-3xyz=0\)

\(\Rightarrow\left(x+y\right)^3-3x^2y-3xy^2+z^3-3xyz=0\)

\(\Rightarrow\left[\left(x+y\right)^3+z^3\right]-3xy\left(x+y+z\right)=0\)

\(\Rightarrow\left(x+y+z\right)\left[\left(x+y\right)^2-\left(x+y\right)z+z^2-3xy\right]=0\)

\(\Rightarrow\left(x+y+z\right)\left(x^2+y^2+z^2-xy-yz-xz\right)=0\)

\(\Rightarrow\frac{1}{2}\left(x+y+z\right)\left[\left(x-y\right)^2+\left(y-z\right)^2+\left(z-x\right)^2\right]=0\)

\(\Rightarrow\left(x-y\right)^2+\left(y-z\right)^2+\left(z-x\right)^2=0\) (do \(x+y+z\ne0\))

\(\Rightarrow\begin{cases}\left(x-y\right)^2=0\\\left(y-z\right)^2=0\\\left(z-x\right)^2=0\end{cases}\)\(\Rightarrow\begin{cases}x-y=0\\y-z=0\\z-x=0\end{cases}\)\(\Rightarrow\begin{cases}x=y\\y=z\\z=x\end{cases}\)\(\Rightarrow x=y=z\)

\(\Rightarrow P=\left(1+\frac{1}{1}\right)\left(1+\frac{1}{1}\right)\left(1+\frac{1}{1}\right)=2\cdot2\cdot2=8\)

8

1/a/
\(A=\frac{2}{xy}+\frac{3}{x^2+y^2}=\left(\frac{1}{xy}+\frac{1}{xy}+\frac{4}{x^2+y^2}\right)-\frac{1}{x^2+y^2}\)

\(\ge\frac{\left(1+1+2\right)^2}{\left(x+y\right)^2}-\frac{1}{\frac{\left(x+y\right)^2}{2}}=16-2=14\)

Dấu = xảy ra khi \(x=y=\frac{1}{2}\)

b/

\(4B=\frac{4}{x^2+y^2}+\frac{8}{xy}+16xy=\left(\frac{4}{x^2+y^2}+\frac{1}{xy}+\frac{1}{xy}\right)+\left(\frac{1}{xy}+16xy\right)+\frac{5}{xy}\)

\(\ge\frac{\left(1+1+2\right)^2}{\left(x+y\right)^2}+2\sqrt{\frac{1}{xy}.16xy}+\frac{5}{\frac{\left(x+y\right)^2}{4}}\)

\(=16+8+20=44\)

\(\Rightarrow B\ge11\)

Dấu = xảy ra khi \(x=y=\frac{1}{2}\)

2/

\(A=\left(x+\frac{1}{x}\right)^2+\left(y+\frac{1}{y}\right)^2\)

\(\ge\frac{\left(x+\frac{1}{x}+y+\frac{1}{y}\right)^2}{2}\ge\frac{\left(1+\frac{4}{x+y}\right)^2}{2}=\frac{25}{2}\)

Dấu = xảy ra khi \(x=y=\frac{1}{2}\)

1, 

trả lời 

a=b=1

cbht

Cho mk lời giải đầy đủ đi