已知x、y、z是实数,a=x²-y,b=y²-z+1/2,c=z²-x+1/3,下列说法正确的是( B)
∵a=x²-y,b=y²-z+1/2,c=z²-x+1/3
a+b+c=x²-x+y²-y+z²-z+1/2+1/3
=x²-x+1/4+y²-y+1/4+z²-z+1/4+1/12
=(x-1/2)²+(y-1/2)²+(z-1/2)²+1/12>0
∴a、b、c中至少有一个是正数
已知x、y、z是实数,a=x²-y,b=y²-z+1/2,c=z²-x+1/3,下列说法正确的是( B)
∵a=x²-y,b=y²-z+1/2,c=z²-x+1/3
a+b+c=x²-x+y²-y+z²-z+1/2+1/3
=x²-x+1/4+y²-y+1/4+z²-z+1/4+1/12
=(x-1/2)²+(y-1/2)²+(z-1/2)²+1/12>0
∴a、b、c中至少有一个是正数