4+12(x-y)+9(x-y)²

4+12(x-y)+9(x-y)^2
=2^2+2*2*[3(x-y)]+[3(x-y)]^2
=[2+3(x-y)]^2
=(3x-3y+2)^2

设a=3(x-y)，则原式化为
2^2+2*2*a+a^2
=（2+a）^2
还原，得（2+3x-3y）^2

4+12(x-y)+9(x-y)²
把(x-y)看做一个未知数A。
则原式=9A²+12A+4=（3A+2）²
因为A=(x-y)²
代入式 中得：原式=（3x-3y+2)²

4+12(x-y)+9(x-y)²
=2^2+2*3(x-y)*2+[3(x-y)]^2
=[2+3(x-y)]^2
=(4+3x-3y)^2

你要求什么啊？