Question

设A=2x方-3xy+y方-x+2y，B=4x方-6xy+2y方+3x-y。若|x-2a|+（y+3）的平方=0，且B-2A=a，求A的值

Answer 1

|x-2a|+(y+3)^2=0
x-2a=0 y+3=0
x=2a y=-3
B-2A
=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
=5x-5y
=10a+15=a
9a=-15
a=-5/3

追问

是求A,不是a!!

追答

x=2a=2*(-5/3)=-10/3
A=2x^2-3xy+y^2-x+2y
=2*(-10/3)^2-3*(-10/3)*(-3)+(-3)^2-(-10/3)+2*(-3)
=200/9-30+9+10/3-6
=230/9-27
=-13/9