Question

这道题怎么做，要详细的答案，感谢了

Answer 1

图姿郑猜迹型丛镇

追问

cos2ξ/2＋sin2ξ/2＝1对吗

Answer 2

cos(π/4-θ/2)=2/3
(√2/2)[ cos(θ/2) + sin(θ/岩桥2) ] =2/3
[ cos(θ/2) + sin(θ/2) ] =2√举枣歼2/3
[ cos(θ/正冲2) + sin(θ/2) ]^2 =8/9
1+sinθ=8/9
sinθ=-1/9
ans :C