a=2/(√3-1)=2(√3+1)/(√3-1)(√3+1)=√3+1
所以a³-a²-a+2
=a²(a-1)-a+2
=(√3+1)²(√3+1-1)-√3-1+2
=(4+2√3)(√3)-√3+1
=4√3+6-√3+1
=7+3√3
如果不懂,请追问,祝学习愉快!三次项系数是2分之1a=2/(√3-1)=2(√3+1)/(√3-1)(√3+1)=√3+1

所以½a³-a²-a+2
=½a²(2a-1)-a+2
=½(√3+1)²(2√3+2-1)-√3-1+2
=(2+√3)(2√3+1)-√3+1
=4√3+2+6+√3-√3+1
=4√3+9