1：(ab+cd)(a²-b²+c²-d²）+(ac+bd)(a²+b²-c²-d²）

题目

1：(ab+cd)(a²-b²+c²-d²）+(ac+bd)(a²+b²-c²-d²）
2：x四次方+2000x²+1999x+2000
3：x²+xy-6y²+x+13y-6
4：x²-2xy+y²-3y+2

答案

1：(ab+cd)(a²-b²+c²-d²）+(ac+bd)(a²+b²-c²-d²)= (ab+cd)(a²-d²)+(ab+cd)(c²-b²)+(ac+bd)(a²-d²)+(ac+bd)((b²-c²)= (a²-d&...