2sin(B/2)=cos(a-c/2) tan(a/2)tan(c/2)=1/3
问题描述：
2sin(B/2)=cos(a-c/2) tan(a/2)tan(c/2)=1/3
2sin(B/2)=cos(a-c/2) tan(a/2)tan(c/2)=1/3是怎么推出了的,
答
B/2=[180-(A+C)]/2=90- (A+C)/2sin(B/2)=cos[(A+C)/2]=cos(A/2)cos(C/2)- sin(A/2)sin(C/2)cos(A-C/2)=cos(A/2)cos(C/2)+sin(A/2)sin(C/2)=2[cos(A/2)cos(C/2)- sin(A/2)sin(C/2)]3sin(A/2)sin(C/2)=cos(A/2)cos(C/2...