If tan2 θ + tan4 θ = 1, then:

cot2 θ + cot4 θ = 1 cos2 θ + cos4 θ = 1 sin2 θ + sin4 θ = 1 cosec2 θ + sec4 θ = 1

cos2 θ + cos4 θ = 1

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