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且B-2A=a,求A的值？ 谁能帮帮我啊！！！

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

Answer 2

解：∵/x-2a/+(y+3)^2=0
∴x=2a y=-3
则A=8a^2+18a+9-2a-6=8a^2+16a+3 B=16a^2+36a+18-6a+3=16a^2+30a+21
B-2A=-2a+15=a
∴a=5
代入A得 A=8*25+80+3=283
答：A=283