Question

设A=2x^2-3xy+y^2-x+2y,B=4x^2-6xy+2y^2+3x-y.若/x-2a/+(y+3)^2=0,

Answer 1

|x-2a|+(y+3)^2=0

x=2a,y=-3

B-2A=a

a=4x^2-6xy+2y^2-3x-y-2(2x^2-3xy+y^2-x+2y)

=4x^2-6xy+2y^2-3x-y-4x^2+6xy-2y^2+2x-4y

=-x-5y

|x-2a|

=|x-2(-x-5y)|

=|x+2x+10y|

=|3x+10y|

=|3x-30|

=0

解得x=10

A=2x^2-3xy+y^2-x+2y

=(x-y)(2x-y)-x+2y

=13×23-10-6

=283