1.已知sin2α=1/4,α属于(π/4,π/2),则 cosα-sinα=?2.已知sinα+cosα=1/3,0<α<π,求
问题描述:
1.已知sin2α=1/4,α属于(π/4,π/2),则 cosα-sinα=?2.已知sinα+cosα=1/3,0<α<π,求
2.求sin2α,cos2α,tan2α
答
1.
(cosα-sinα)^2
=1-2sinαcosα
=1-sin2α
=1-1/4
=3/4
而 α∈(π/4,π/2)时,cosα