Help!!數學暑期作業問題(20分)

1)sin^4θ-cos^4θ=1-2cos^2θL.H.S.= (sin^2 θ + cos^2 θ)(sin^2 θ - cos^2 θ)= sin^2 θ - cos^2 θ= (1 - cos^2 θ) - cos^2 θ= 1 - 2cos^2 θ= R.H.S. 2)(1+tanθ)^2-2tanθ=1/(1-sinθ)(1+sinθ)L.H.S.= (1 + 2tanθ + tan^2 θ) - 2tanθ= 1 + tan^2 θ= 1 + (sin^2 θ) / cos^2 θ= (cos^2 θ + sin^2 θ) / cos^2 θ= 1 / cos^2 θ)= 1 / (1 - sin^2 θ)= 1 / [(1-sinθ)(1+sinθ)]= R.H.S.