2sin(B/2)=cos(a-c/2) tan(a/2)tan(c/2)=1/32sin(B/2)=cos(a-c/2) tan(a/2)tan(c/2)=1/3是怎么推出了的,

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2sin(B/2)=cos(a-c/2) tan(a/2)tan(c/2)=1/32sin(B/2)=cos(a-c/2) tan(a/2)tan(c/2)=1/3是怎么推出了的,
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2sin(B/2)=cos(a-c/2) tan(a/2)tan(c/2)=1/32sin(B/2)=cos(a-c/2) tan(a/2)tan(c/2)=1/3是怎么推出了的,
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,

2sin(B/2)=cos(a-c/2) tan(a/2)tan(c/2)=1/32sin(B/2)=cos(a-c/2) tan(a/2)tan(c/2)=1/3是怎么推出了的,
B/2=[180-(A+C)]/2=90- (A+C)/2
sin(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)
[sin(A/2)sin(C/2)] /cos(A/2)cos(C/2)= 1/3
tan(A/2)tan(C/2)=1/3