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问题: 代数小小问题

(5+2倍根号3)(5-2倍根号3)-(2倍根号7-1)2=?

解答:

(5+2√3)(5-2√3)-(2√7-1)2=
5^2-(2√3)^2-(2√7-1)^2=
25-12-[(2√7)^2-4√7+1]=
13-[28-4√7+1]=
-16+4√7