Answer
See below.
Work Step by Step
1. $LHS=sec^4\theta-sec^2\theta=sec^2\theta(sec^2\theta-1)=sec^2\theta(tan^2\theta)$
2. $RHS=tan^4\theta+tan^2\theta=tan^2\theta(tan^2\theta+1)=tan^2\theta(sec^2\theta)=LHS$
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