已知sin(π/6-α)=1/5,且α∈(0,π/2),则cosα=
问题描述：
已知sin(π/6-α)=1/5,且α∈(0,π/2),则cosα=
答
解α∈(0,π/2)知-α∈(-π/2,0)π/6-α∈(-π/3,π/6)由sin(π/6-α)=1/5知π/6-α是第一象限角即cos(π/6-α)=2√6/5cosα=cos-α=cos[(π/6-α）-π/6]=cos(π/6-α）cos(π/6）+sin(π/6-α）sin(π/6）=2√6/5...