Back referencing equations

[Paul Medwell]

I have an equation in Chapter 1 that I would like to repeat in Chapter 2. How can I get the equation (AND its equation number reference) to appear in the second chapter exactly the same as it appears in chapter 1?

Example:

Chapter 1
This is my equation:
y=2x (1.1)

Chapter 2
As was shown in Chapter 1:
y=2x (1.1)

Then later, if the equation in Chapter 1 changes, it will automatically change in Chapter 2.

Cheers,
Paul