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

题目

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

答案

1.
(cosα-sinα)^2
=1-2sinαcosα
=1-sin2α
=1-1/4
=3/4
而 α∈(π/4,π/2)时,cosα