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(1+tan21°)(1+tan22°)(1+tan23°)(1+tan24°)的值是.

题目详情
(1+tan21°)(1+tan22°)(1+tan23°)(1+tan24°)的值是 ______.
▼优质解答
答案和解析
根据tan45°=tan(21°+24°)=
tan21°+tan24°
1−tan21°tan24°
=1
得到tan21°+tan24°=1-tan21°tan24°①;同理得到tan22°+tan23°=1-tan22°tan23°②;
则原式=[(1+tan21°)(1+tan24°)][(1+tan22°)(1+tan23°)]
=(1+tan24°+tan21°+tan24°tan21°)(1+tan22°+tan23°+tan22°tan23°)
=(1+1-tan24°tan21°+tan24°tan21°)(1+1-tan22°tan23°+tan22°tan23°)=4
故答案为:4.