![](https://iknow-base.cdn.bcebos.com/lxb/notice.png)
已知x²-4x-1=0求代数式(2x-3)²-(x+y)(x-y)-y²的值
1个回答
展开全部
你好,这种题型考察的是整体代入
如果你方程的解则很复杂
解:
x²-4x-1=0
x²-4x=1
于是
(2x-3)²-(x+y)(x-y)-y²
=4x²-12x+9-(x²-y²)-y²
=4x²-12x+9-x²+y²-y²
=3x²-12x+9
=3(x²-4x)+9
=3*1+9
=12
如果你方程的解则很复杂
解:
x²-4x-1=0
x²-4x=1
于是
(2x-3)²-(x+y)(x-y)-y²
=4x²-12x+9-(x²-y²)-y²
=4x²-12x+9-x²+y²-y²
=3x²-12x+9
=3(x²-4x)+9
=3*1+9
=12
推荐律师服务:
若未解决您的问题,请您详细描述您的问题,通过百度律临进行免费专业咨询