sinα2=±1−cosα2 sin\frac{\alpha}{2} = \pm\sqrt{\frac{1-cos\alpha}{2}}

    cosα2=±1+cosα2 cos\frac{\alpha}{2} = \pm\sqrt{\frac{1+cos\alpha}{2}}

    tanα2=±1−cosα1+cosα=1−cosαsinα=sinα1+cosα tan\frac{\alpha}{2} = \pm\sqrt{\frac{1-cos\alpha}{1+cos\alpha}} = \frac{1-cos\alpha}{sin\alpha} = \frac{sin\alpha}{1+cos\alpha}