solve ax+b=0 急!! plz help 20點!

1、If a=0 , then b=0, x can be any real number.

eg.
(0)x+b=0
0+b=0
b=0

2、If a≠0, then x=-b/a, and b can be any real number.

eg.
2x+b=0
2x=-b
x=-b/2

if there is any problem please comment~

should we consider the case when a=0 and b<>0 as well ?

"don't tell me that x= -b/a"

Then what should I tell you?????