# About method of work and Energy or Clapeyron theorem

I'm having some difficulty to understand the work and Energy method (aka Clapeyron theorem), especially with different loads.

Could you please help me to fix this problem, because I found different formula of Work and Energy method:

$$U(F_i)= \frac{1}{2}\sum_{i=1}^n Fi \cdot \Delta_{i=1}$$

and

$$U(F)= \frac{1}{2}F \cdot \Delta_{}$$

Is this method applicable using different loads or only for one?