已知sin2θ=1/3,且π/4<θ<π/2,那么cosθ-sinθ=
问题描述:
已知sin2θ=1/3,且π/4<θ<π/2,那么cosθ-sinθ=
答
(cosθ-sinθ)²
=sin²θ+cos²θ-2sinθcosθ
=1-sin2θ
=2/3
∵π/4<θ<π/2
∴cosθ