已知：x+y=12,xy=9,
则x²+3xy+2y²/x²y+2xy²=(x+y)(x+2y)/[xy(x+2y)]
=(x+y)/xy=12/9=4/3 .
已知：3x-2y-4z=0,x+y-3z=0,且xyz≠0,
则：3x-2y＝4z,2x+2y＝6z,3x+3y＝9z
∴ 5x=10z, x=2z.
∴ 5y=5z,y=z,
5x²-3y²+12z²/2x²+7y²+10z²=[5*(2z)²-3*z²+12z²]/[2*(2z)²+7z²+10z²]
= 29z²/25z²=29/25