# Ising model and duality

I'm studying the Ising model in 2 dimensions in an approximative way. Now my professor has written this formula that links the dual space and the "normal" space:

$$\sinh(2 K) \sinh(2 K^*) = 1$$

Do you know how can I demonstrate this equivalence?

• I'm going to suggest that your question would be clearer to many readers if you edited it to include a definition of $K$, and perhaps a bit more background about the context in which this equation has arisen. – user197851 Dec 11 '18 at 22:27