[Grammar] article after adjective

[Azah]

1) a. I have as good a voice as you.
b. I have as good as you.
2) a. She is too polite a person to refuse.
b. She is too polite person to refuse.

In a, article has been placed after adjectives, while in case of b, article has not been used. Please tell me the differences between a and b. When articles are used after adjectives?

 

[SoothingDave]

A is correct. B is incorrect.

 

[Roman55]

I am not a teacher.

1a and 2a are correct sentences. 1b and 2b aren't.

Edit: Cross-posted with SoothingDave