2) The original formula =x? -xy-8xy+8y？ =x？ -9xy+8y？

3) The original formula =x? +2xy+y？

4) The original formula =x? y^4+xy？ +x？ y^5+y？

5) The original formula =x? +x？ +x-x？ -x- 1=x？ +x- 1