\(A=\frac{a\left(a+b^2\right)-ab^2}{a+b^2}+\frac{b\left(b+c^2\right)-bc^2}{b+c^2}+\frac{c\left(c+a^2\right)-ca^2}{c+a^2}\)
\(A=a+b+c-\left(\frac{ab^2}{a+b^2}+\frac{bc^2}{b+c^2}+\frac{ca^2}{c+a^2}\right)\)
\(A\ge3-\left(\frac{ab^2}{2\sqrt{ab^2}}+\frac{bc^2}{2\sqrt{bc^2}}+\frac{ca^2}{2\sqrt{ca^2}}\right)\)
\(A\ge3-\frac{1}{2}\left(\sqrt{a}.b+\sqrt{b}.c+\sqrt{c}.a\right)\)
\(A\ge3-\frac{1}{2}\left(\frac{b\left(a+1\right)}{2}+\frac{c\left(b+1\right)}{2}+\frac{a\left(c+1\right)}{2}\right)\)
\(A\ge3-\frac{1}{4}\left(ab+bc+ca+a+b+c\right)\)
\(A\ge3-\frac{1}{4}\left(3+\frac{\left(a+b+c\right)^2}{3}\right)\) \(=3-\frac{3}{2}=\frac{3}{2}\)
Min \(A=\frac{3}{2}\) \(\Leftrightarrow a=b=c=1\)
