已知sinθ=1/3,0

问题描述:

已知sinθ=1/3,0

cosθ=√(1-sin²θ)=2√2/3
sin2θ=2sinθcosθ=2*1/3*2√2/3=4√2/9
cos2θ=cos²θ-sin²θ=8/9-1/9=7/9