如果9x^2-(4a+3b)xy-(a+2b)y^2=(3x-y)^2,求a^3-4a^2b+4ab^2
问题描述：
如果9x^2-(4a+3b)xy-(a+2b)y^2=(3x-y)^2,求a^3-4a^2b+4ab^2
答
即9x^2-(4a+3b)xy-(a+2b)y^2=9x^2-6xy+y^2
所以-(4a+3b)=-6
-(a+2b)=1
所以b=-2,a=3
所以原式=a(a²-4ab+4b²)
=a(a-2b)²
=3*7²
=147