2(x-y)-4(-y-x)

2(x-y)-4(-y-x)
=2x-2y+4y+4x
=6x+2y
=2(3x+y)

用分配率
2(x-y)-4(-y-x)
=2x-2y+4y+4x
=6x+2y
=2(3x+y)
再提公因式2得：3x+y

2(x-y)-4(-y-x)=2x-2y+4y+4x=6x+2y=2（3x+y）
公因式是2

2(x-y)-4(-y-x)可将括号去掉得 2x-2y+4y+4x
在合并同类项得2（3x-y)

2（3x-y)

2(x-y)-4(-y-x)=2x-2y+4y+4x=6x+2y=2(3x+y)