Question

tan(a/2)=sina/(1+cosa)=(1-cosa)/sina

Answer 1

证明：sina/(1+cosa)=2sin(a/2)cos(a/2)/2cos(a/2)*cos(a/2)=tan(a/2)(1-cosa)/sina=2sin(a/2)*sin(a/2)/2sin(a/2)cos(a/2)=tan(a/2)所以tan(a/2)=sina/(1+cosa)=(1-cosa)/sina