(x+y+z)^2=x^2+y^2+z^2+2(xy+yz+zx)
=x^2+y^2+z^2+2
=(x^2+y^2)/2+(y^2+z^2)/2+(x^2+z^2)/2+2
≥2[√(x^2*y^2)]/2+2[√(y^2*z^2)]/2+2[√(x^2*z^2)]/2+2
=xy+yz+zx+2
=3
(x+y+z)^2≥3
x+y+z≥√3.
(x+y+z)^2=x^2+y^2+z^2+2(xy+yz+zx)
=x^2+y^2+z^2+2
=(x^2+y^2)/2+(y^2+z^2)/2+(x^2+z^2)/2+2
≥2[√(x^2*y^2)]/2+2[√(y^2*z^2)]/2+2[√(x^2*z^2)]/2+2
=xy+yz+zx+2
=3
(x+y+z)^2≥3
x+y+z≥√3.