一题：（3x-2y)^2-(2x+3y)^2

一题： （3x-2y)^2-(2x+3y)^2
=(3x-2y+2x+3y)(3x-2y-2x-3y)
=(5x+y)(x-5y)
二题： 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.
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 )
=-3x+2x-y-4y
=-x-5y=a
-2a+15=a
a=5
x=2a=10
A=2x^2-3xy+y^2-x+2y =(2x-y)(x-y)-x+2y
=(20+3)(10+3)-10-6
=299-16
=283