Answer: A straight line must pass through B. If a.b.c has no negative value, the triangle is an equilateral triangle. Negative values cannot form triangles.

Arrange (a+b)/c=(b+c)/a=(c+a)/b=p, A+B = CP, B+C = AP, C+A = BP, and add them to get 2 (a+b+c) = (a+b+c) p.