\(A=\frac{a}{b+c-a}+\frac{b}{a+c-b}+\frac{c}{a+b-c}\)
\(=\frac{a^2}{ab+ac-a^2}+\frac{b^2}{ba+bc-b^2}+\frac{c^2}{ca+cb-c^2}\)
\(\ge\frac{\left(a+b+c\right)^2}{2\left(ab+bc+ca\right)-\left(a^2+b^2+c^2\right)}\)
\(\ge\frac{\left(a+b+c\right)^2}{\frac{2\left(a+b+c\right)^2}{3}-\frac{\left(a+b+c\right)^2}{3}}=3\)