题目

已知=1,求证:=1. 答案：证法一:∵=1,∴cos4A·sin2B+sin4A·cos2B=sin2B·cos2B.∴cos4A(1-cos2B)+sin4A·cos2B=(1-cos2B)cos2B,即cos4A-cos2B(cos4A-sin4A)=cos2B-cos4B.∴cos4A-2cos2Acos2B+cos4B=0.∴(cos2A-cos2B)2=0.∴cos2A=cos2B.∴sin2A=sin2B.∴=cos2B+sin2B=1.证法二:令=cosα,=sinα,则cos2A=cosBcosα,sin2A=sinBsinα.两式相加,得1=cosBcosα+sinBsinα,即cos(B-α)=1.∴B-α=2kπ(k∈Z),即B=2kπ+α(k∈Z).∴c李白诗歌的主要内容和艺术特点是什么？为什么会具有这些特点？________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________