Question

已知x的平方-5x+1=0,求x的三次方-4x的平方-1的值?

怎么不回答啊？

Answer 1

x的平方-5x+1=0,
x²=5x-1

x的三次方-4x的平方-1
=x(5x-1)-4x²-1
=5x²-5x-4x²-1
=x²-5x-1
=5x-1-5x-1
=-2

追问

=x(5x-1)-4x²-1
=5x²-5x-4x²-1
这个对吗？

追答

对啊
=x(5x-1)-4x²-1
把x代入括号
=5x²-5x-4x²-1
合并同类项得：
=x²-5x-1
=5x-1-5x-1
=-2

追问

=x(5x-1)-4x²-1
=5x²-5x-4x²-1
把x代入得到5x的平方-x啊，怎么是=5x²-5x-4x²-1

追答

哈哈，是的，我看错了，不好意思
=x(5x-1)-4x²-1
=5x²-x-4x²-1
=x²-x-1
=5x-1-x-1
=4x-2

Answer 2

x的平方-x-1