已知sin(a/2)=4/5,a∈(π,2π),求sina,cosa,tana.

网友回答

a∈(π,2π)
a/2∈(π/2,π)
sin(a/2)=4/5
cos(a/2)=-3/5
sina=2sin(a/2)cos(a/2)
=2*4/5*(-3/5)
=-24/25
cosa=1-2sin²(a/2)
=1-2*16/25
=-7/25
tana=sina/cosa
=(-24/25)/(-7/25)
=24/7======以下答案可供参考======
供参考答案1:
sina=2sin(a/2)cos(a/2)
=-24/25cosa=1-2[sin(a/2)]^2=-7/25
tana=sina/cosa
=24/7