sec^4(x) - tan^4(x) =
= (1 + tan^2(x))^2 - tan^4(x)
= 1 + 2tan^2(x) + tan^4(x) - tan^4(x)
= 1 + 2tan^2(x)
QED
Use Trig identities to verify that sec^4(x)-tan^4(x)=1+2tan^2(x), Only work with one side of the equation
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