a + b + c = 0, then the value of $$\frac{{{a^2} + {b^2} + {c^2}}}{{ab + bc + ca}}$$   is?

$$\eqalign{ & {\text{If }}a + b + c = 0 \cr & {\text{Put }}a = 1,{\text{ }}b = 1{\text{ and }}c = - 2 \cr & \therefore \frac{{{a^2} + {b^2} + {c^2}}}{{ab + bc + ca}} \cr & = \frac{{1 + 1 + 4}}{{1 - 2 - 2}} \cr & = \frac{6}{{ - 3}} \cr & = - 2 \cr} $$