∵∠ABC的外角平分线是x=0,∴点B在y轴上,∵∠ACB的内角平分线是y=3x,∴点C在直线y=3x上,设B(0,b),C(c,3c)(c≠0),∵A(2,1),∴直线AB、AC、BC的斜率分别为K(AB)=(b-1)/(0-2)=-(b-1)/2,K(AC)=(3c-1)/(c-2),K(BC)=(3c-b)...