Cho a + b + c = 0

Câu hỏi: Cho a + b + c = 0 $\left(\mathrm{a}\ne 0,\mathrm{b}\ne 0,\mathrm{c}\ne 0\right)$. Tính giá trị biểu thức: $\mathrm{A}=\frac{{\mathrm{a}}^2}{{\mathrm{a}}^2-{\mathrm{b}}^2-{\mathrm{c}}^2}+\frac{{\mathrm{b}}^2}{{\mathrm{b}}^2-{\mathrm{c}}^2-{\mathrm{a}}^2}$$+\frac{{\mathrm{c}}^2}{{\mathrm{c}}^2-{\mathrm{a}}^2-{\mathrm{b}}^2}$