____      ____

____>____

根据短文理解，完成下列各题。

    My name is Kitty. I have a very big and nice room and I have a great school things collection.

My brother's room is near my room. He is Mike. And he has a big sports collection. I have twenty erasers, ten pencils, nine rulers and eight pens in my schoolbag. My brother has two baseballs, four soccer balls and five basketballs under his bed.

下面是某同学对多项式（x²﹣4x+2）（x²﹣4x+6）+4进行因式分解的过程．

解：设x²﹣4x=y

原式=（y+2）（y+6）+4（第一步）

=y²+8y+16（第二步）

=（y+4）²（第三步）

=（x²﹣4x+4）²（第四步）

请问：