问题:
已知sinα=
12
13
,sin(α+β)=
4
5
,α与β均为锐角,求cos
β
2
.(cos
β
2
=±
1+cosβ
2
)
已知sinα=
,sin(α+β)=
,α与β均为锐角,求cos
.(cos
=±
)
12 |
13 |
4 |
5 |
β |
2 |
β |
2 |
|
参考答案: