问题
选择题
若
|
答案
∵cos2θ=cos2θ-sin2θ，1+sin2θ=sin2θ+2sinθcosθ+cos2θ
∴
=cos2θ 1+sin2θ cos 2θ-sin 2θ sin 2θ+2sinθcosθ+cos 2θ
分子、分母都除以cos2θ，得
=cos2θ 1+sin2θ 1-tan2θ tan2θ+2tanθ+1
∵
=1，解之得tanθ=-1-tanθ 2+tanθ 1 2
∴代入
=cos2θ 1+sin2θ
得1-tan2θ tan2θ+2tanθ+1
=cos2θ 1+sin2θ
=31-(-
)21 2 (-
)2+2×(-1 2
)+11 2
故选：A