B＝π/3
是三角形吧。asin[(A+C)/2] = bsinA, asin[(π-B)/2] = bsinA,acos(B/2) = bsinA， a/sinA = b/cos(B/2),又 a/sinA = b/sinB, 则 sinB = cos(B/2)，2sin(B/2)cos(B/2) = co...
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