已知实数x,y,z适合x+y=6,z^2=xy-9,求z的值

问题描述:

已知实数x,y,z适合x+y=6,z^2=xy-9,求z的值
要有过程或思路,能看懂就行

X=6-Y,--(1)
Z^2=XY-9--(2)
1代入2得:
Z^2=6Y-Y^2-9
Z^2+(Y^2-6Y+9)=0
Z^2+(Y-3)^2=0
因为Z^2大于等于0,(Y-3)^2大于等于0
所以..
Z^2=0 (Y-3)^2=0
Z=0 Y=3 X=3