\(x+y+z=0< =>\left(x+y+z\right)^2=0< =>x^2+y^2+z^2+2\left(xy+yz+zx\right)=0\)
\(< =>x^2+y^2+z^2=0< =>x=y=z=0\)
\(B=\left(-1\right)^{2007}+0+1^{2009}=0\)
x+y+z=0
\(\Rightarrow\left(x+y+z\right)^2=0\Leftrightarrow x^2+y^2+z^2+2\left(xy+yz+xz\right)=0\)
\(\Leftrightarrow x^2+y^2+z^2=0\)( vì xy+yz+zx=0)
Mà \(x^2+y^2+z^2\ge0\forall x,y,z\Rightarrow x=y=z=0\)
\(\Rightarrow B=\left(0-1\right)^{2007}+0^{2008}+\left(0+1\right)^{2009}\)
= -1+0+1=0
Vậy B=0
