Question

已知:有理数x,y,z,满足x=6-y,z的2次方=xy-9,求证x=y.

Answer 1

x=6-y

z的平方=xy-9=(6-y)y-9=-y^2+6y-9=-(y-3)^2

z^2+(y-3)^2=0

要使等号成立,必须z=0 y-3=0

所以y=3

x=6-y=3

即x=y