已知a=-2/(根号7)+3,=-2(3-√7)/(9-7)=-(3-√7)=√7-3;求代数式a^3+5a^2-4a-6的值=a²(a+5)-4a-6=(7+3-6√7)(√7+2)-4√7+12-6=10√7+20-42-12√7+6-4√7=-6√7-16;您好,很高兴为您解答,skyhunter002为您答疑解...-2/(根号7)+3=√7-6吧-2/(√7+3)=-2(3-√7)/(3+√7)(3-7)=-2(3-√7)/2=√7-3;