If sin4(θ)−cos4(θ)=k\sin^4(\theta) - \cos^4(\theta) = ksin4(θ)−cos4(θ)=k, then what is the value of cos(2θ)\cos(2\theta)cos(2θ)?
−k-k−k
kkk
1−k1-k1−k
k−1k-1k−1