证明:1-2(secα)^2=(tanα)^4-(secα)^4

问题描述:

证明:1-2(secα)^2=(tanα)^4-(secα)^4

(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