原式=[(1tan21°)(1+tan24°)][(1+tan22°)(1+tan23°)]
=(1+tan21°+tan24°+tan24°tan21°)(1+tan22°+tan23°+tan22°tan23°)
=[1+tan45°(1-tan21°tan24°)+tan21°tan24°][1+tan45°(1-tan23°tan22°+tan22°tan23°]
=(1+1)(1+1)(tan21°tan24°可消掉,tan23°tan22°同样)
=4
正确答案应该是4吧
思路是:21°+24°=45°22°+23°=45°