设x=二分之根五减一,求x的四次方+x²+2x-1
问题描述：
设x=二分之根五减一,求x的四次方+x²+2x-1
答
即2x+1=√5
平方
4x²+4x+1=5
x²=1-x
所以x^4
=(1-x)²
=1-2x+x²
=(1-2x)+(1-x)
=2-3x
所以原式=(2-3x)+(1-x)+2x-1
=2-2x
=2-2(√5-1)/2
=3-√5