已知x=2-根号3,则根号下x^3-5x^2+5x+7=

问题描述:

已知x=2-根号3,则根号下x^3-5x^2+5x+7=

2-x=√3
x^2-4x+4=3
x^2-4x=-1
x三次方-5x二次方+5x+7
=[x^3-4x^2]-[x^2-4x]+x+7
=-x+1+x+7
=8
根号下x三次方-5x二次方+5x+7
=2√2