Toán 10 CMR: xy(z+2x)+yz(x+2y)+zx(y+2)3 \frac{x}{\sqrt{y(z+2x)}}+\frac{y}{\sqrt{z(x+2y)}}+\frac{z}{\sqrt{x(y+2)}} \geq \sqrt{3}

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x3y(z+2x)+y3z(x+2y)+z3x(y+2)2x2x+3y+z+2yx+2y+3z+2z3x+y+2z=2(x22x2+3xy+zx+y2xy+2y2+3yz+z23xz+yz+2z2)2.(x+y+z)22x2+2y2+2z2+4xy+4yz+4zx=2(x+y+z)22(x+y+z)2=1xy(z+2x)+yz(x+2y)+zx(y+2)3\frac{x}{\sqrt{3y(z+2x)}}+\frac{y}{\sqrt{3z(x+2y)}}+\frac{z}{\sqrt{3x(y+2)}} \geq \frac{2x}{2x+3y+z}+\frac{2y}{x+2y+3z}+\frac{2z}{3x+y+2z}=2(\frac{x^2}{2x^2+3xy+zx}+\frac{y^2}{xy+2y^2+3yz}+\frac{z^2}{3xz+yz+2z^2})\geq 2.\frac{(x+y+z)^2}{2x^2+2y^2+2z^2+4xy+4yz+4zx}=\frac{2(x+y+z)^2}{2(x+y+z)^2}=1\Rightarrow \frac{x}{\sqrt{y(z+2x)}}+\frac{y}{\sqrt{z(x+2y)}}+\frac{z}{\sqrt{x(y+2)}} \geq \sqrt{3}
 
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