已知a=根号3-1,求a立方+2a平方-a的值
a立方+2a平方-a
=a³+2a²+a-2a
=a(a²+2a+1)-2a
=a(a+1)²-2a
=(√3-1)(√3-1+1)²-2(√3-1)
=3√3-3-2√3+2
=√3-1