If tan2 θ + tan4 θ = 1, then:

Given :-

tan² θ + tan⁴ θ = 1  ----(1)

tan² θ( 1 + tan² θ ) = 1

tan² θ . sec² θ = 1

tan² θ = cos² θ

Put value of  tan² θ in equation 1 

So , cos² θ + cos⁴ θ = 1 , option 2 is correct