将z看成已知数4x+5y=6z①x+2y=7z②可解得②×4-①可得3y=22zy=22/3zx=7z-2y=-23/3z代入计算式有计算式=[2*(-23/3)²+(22/3)²-6]z²/{[(-23/3)²+5*(22/3)²+3]z²}=(2*23²+22²-6*3²)/(23²+5*22²+3*3²)=1488/2976=1/2
