设x,y,z∈R+.求证:x^4+y^4+z^4≥(x+y+z)xyz

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设x,y,z∈R+.求证:x^4+y^4+z^4≥(x+y+z)xyz

设x,y,z∈R+.求证:x^4+y^4+z^4≥(x+y+z)xyz
设x,y,z∈R+.求证:x^4+y^4+z^4≥(x+y+z)xyz

设x,y,z∈R+.求证:x^4+y^4+z^4≥(x+y+z)xyz
x^4+y^4≥2x²y²
y^4+z^4≥2y²z²
z^4+x^4≥2z²x²
三式相加得x^4+y^4+z^4≥x²y²+y²z²+z²x²
x²y²+y²z²≥2xy²z
y²z²+z²x²≥2xyz²
z²x²+x²y²≥2x²yz
三式相加得x²y²+y²z²+z²x²≥xy²z+xyz²+x²yz=(x+y+z)xyz

x^4+y^4≥2x2y2
y^4+z^4≥2y2z2
z^4+x^4≥2z2x2
三式相加得x^4+y^4+z^4≥x2y2+y2z2+z2x2
x2y2+y2z2≥2xy2z
y2z2+z2x2≥2xyz2
z2x2+x2y2≥2x2yz
三式相加得x2y2+y2z2+z2x2≥xy2z+xyz2+x2yz=(x+y+z)xyz
等号成立则x=y=z