问题标题：
证明:1-2(secα)^2=(tanα)^4-(secα)^4
问题描述：
证明:1-2(secα)^2=(tanα)^4-(secα)^4
马允胜回答：
(tanα)^4-(secα)^4
=(tan^a-sec^2a)(tan^a+sec^2a)
=-(tan^a+sec^2a)
=-(sec^2a-1+sec^2a)
=1-2(secα)^2
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