已知x-4y-5z=0,-3x+y+4z=0（xyz≠0）则xy/z^2=

Question

已知x-4y-5z=0,-3x+y+4z=0（xyz≠0）则xy/z^2=

Answer 1

x-4y-5z=0①,-3x+y+4z=0②
①×3+②得：-11y-11z=0解得y=-z
把y=-z代入①得：x+4z-5z=0解得x=z
所以xy/z^2=z×（-z）/z²=-z²/z²=-1