Elesticity - What must be true about the demand function if E=0?

[gillgill]

What must be true about the demand function if E=0?
i know that E=0 is perfectly inelastic. What is it about the demand function?

 

[HallsofIvy]

What must be true about the demand function if E=0?
i know that E=0 is perfectly inelastic. What is it about the demand function?

No, you don't know that. "E= 0" is perfectly constant, not "perfectly inelastic"! If E, the "elasticity of demand", is 0 then, by definition of E, it is the demand that is "perfectly inelastic". Review your books definition of "E".