2x-3y-z=0 1
X+3Y-14Z=02
1式+2式:3x-15z=0 即x=5z3
1式-2*2式: -9y+27z=0 即 3z=y 4
3式/4式:x/y=5/3即x=5y/3
(4x^2-5xy+z^2)÷(xy+yz+xz)
=[4x^2-5x*3x/5+(x/5)^2]÷(15z^2+3z^2+5z^2)
=(4x^2-3x^2+x^2/25）÷23z^2
=(26x^2/25）÷23z^2 由3式x/z=5(x/z）^2=25
=26/23