(a^2+b^2-c^2)^2-4a^2b^2=[(a^2+b^2-c^2)+2ab][(a^2+b^2-c^2)-2ab]=(a²+2ab+b²-c²)(a²-2ab+b²-c²)=(a+b-c)(a+b+c)(a-b+c)(a-b-c)∵abc是三角形ABC的三边，∴a+b-c>0a+b+c>0a-b+c>0,a-b-c<0,∴(a^2+b^2-c^2)^2-4a^2b^2<0,
