x+y=3,xy=2,则(5x-2)=( ),-(3xy-5y)=( )
问题描述：
x+y=3,xy=2,则(5x-2)=( ),-(3xy-5y)=( )
答
x+y=3,y=3-x
xy=2,
x(3-x)=2
3x-x^2=2
x^2-3x+2=0
(x-1)(x-2)=0
x=1或2
y=2或1 5x-2=3或8 -(3xy-5y)=-(6-5)或-(6-10) -(3xy-5y)=-1或4