Question

若sin2α=1/4,π/4<α<π/2,则cosα-sinα=?

Answer 1

(cosα-sinα)^2=cos^2α+sin^2-2sinαcosα=1-1/4=3/4因为π/4<α<π/2，所以cosα-sinα<0,所以cosα-sinα=-√3/2

Answer 2

2*sin a*cos a=1/4;
(sin a)^2+(cos a)^2=1;
联立，解得。