x分之3=y分之1
x=3y
y分之1=z分之2
z=2y
xy+yz+zx分之2x²-2y²+5z²
=[2(3y)²-2y²+5(2y)²]/(3y*y+y*2y+3y*2y)
=(18y²-2y²+20y²)/(3y²+2y²+6y²)
=36y²/11y²
=36/11
如果本题有什么不明白可以追问,