S(PBC)=6。因为S(PAB):S(PBC):S(PCA)=2:3:4。3PA,4PB和2PC成闭合三角形,设闭合三角形面积为St3PA x 4PB x sinAPB=4PB x 2PC x sinBPC=2PC x 3PA x sinCPA=2St。而S(PAB)=1/2 x PA x PB x sinAPB=1/2 x 2St x 1/3 x 1/4,S(PBC)=1/2 x PB x PC x sinBPC,S(CPA)=1/2 x PC x PA x sinCPA,然后你懂的。...