199. Find the conditions that the parameters $a, b, c$ of the equation $a x=b-c$ must satisfy for the equation to have: 1) a positive root, 2) a negative root, 3) a root equal to zero.
Instruction. 1) when $a>0, b>c$ or when $a>0, c<b$;
2) when $a<0, b>c$ or when $a<0, c>b$;
3) when $a \neq 0, b=c$.