cosθ1+sinθ+1+sinθcosθ
=cosθ(1−sinθ)(1−sinθ)(1+sinθ)+1+sinθcosθ
=cosθ(1−sinθ)1−sin2θ+1+sinθcosθ
=cosθ(1−sinθ)cos2θ+1+sinθcosθ
=1−sinθcosθ+1+sinθcosθ
=1cosθ−sinθcosθ+1cosθ+sinθcosθ
=2cosθ=2secθ
Alternative
cosθ1+sinθ+1+sinθcosθ
=cos2θ+(1+sinθ)2(1+sinθ)cosθ
=cos2θ+(1+2sinθ+sin2θ)(1+sinθ)cosθ
=2+2sinθ(1+sinθ)cosθ
=2cosθ=2secθ