已知x²-4x-1=0求代数式(2x-3)²-(x+y)(x-y)-y²的值为什么不能算出x²-4x-1=0的值?
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![已知x²-4x-1=0求代数式(2x-3)²-(x+y)(x-y)-y²的值为什么不能算出x²-4x-1=0的值?](/uploads/image/z/1143954-18-4.jpg?t=%E5%B7%B2%E7%9F%A5x%26%23178%3B-4x-1%3D0%E6%B1%82%E4%BB%A3%E6%95%B0%E5%BC%8F%EF%BC%882x-3%29%26%23178%3B-%EF%BC%88x%2By%EF%BC%89%EF%BC%88x-y%EF%BC%89-y%26%23178%3B%E7%9A%84%E5%80%BC%E4%B8%BA%E4%BB%80%E4%B9%88%E4%B8%8D%E8%83%BD%E7%AE%97%E5%87%BAx%26%23178%3B-4x-1%3D0%E7%9A%84%E5%80%BC%3F)
已知x²-4x-1=0求代数式(2x-3)²-(x+y)(x-y)-y²的值为什么不能算出x²-4x-1=0的值?
已知x²-4x-1=0求代数式(2x-3)²-(x+y)(x-y)-y²的值
为什么不能算出x²-4x-1=0的值?
已知x²-4x-1=0求代数式(2x-3)²-(x+y)(x-y)-y²的值为什么不能算出x²-4x-1=0的值?
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
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