If tan θ = abthen(cos θ+sin θ)(cos θ−sin θ) = ?
(a) a+ba−b (b) a−ba+b (c) b+ab−a (d) b−ab+a
tan θ =ab
sinθcosθ = ab------(1)
LHS = cosθ+sinθcosθ−sinθ
dividing each term with cosθ
= cosθcosθ+sinθcosθcosθcosθ−sinθcosθ
=sinθcosθ+11−sinθcosθ
=ab+11−ab
=(b+a)(b−a)