已知a=(5-根号21)/2,求代数式a(a-1)(a-2)(a-3)(a-4)(a-5)的值
问题描述：
已知a=(5-根号21)/2,求代数式a(a-1)(a-2)(a-3)(a-4)(a-5)的值
答
∵a=(5-根号21)/2∴2a-5=-√21∴4a²-20a+25=21∴a²-5a+1=0∴a²-5a=-1,a(a-1)(a-2)(a-3)(a-4)(a-5)=a(a-5)(a-2)(a-3)(a-1)(a-4)=(a²-5a)(a²-5a+6)(a²-5a+4)=-1×(-1+6)×(-1+4)=-15...