Question

How to show a demand curve which have constant elasticity of demand ?

Answer 1

I don't remember this, so have automatically done an Internet search (for "a demand curve which have constant elasticity of demand").

One of the more promising / helpful sites I found that way has this URL:

https://www.khanacademy.org/economics-finance-domain/microeconomics/elasticity-tutorial/price-elasticity-tutorial/v/constant-unit-elasticity

I'd suggest you watch this video for further information.