Since the question is unclear, we assume as follows:
Show that cosθ+sinθcosθ−sinθ=sec2θ−tan2θ .
cosθ+sinθcosθ−sinθ
multiplying and dividing by \cos \theta-\sin \theta
=cosθ+sinθcosθ−sinθ×cosθ−sinθcosθ−sinθ
simplifying and using trigonometric identities
=cos2θ−sin2θ(cosθ−sinθ)2=cos2θcos2θ+sin2θ−2sinθcosθ=cos2θ1−sin2θ=sec2θ−tan2θ
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