# Minimal of free energy equation

## Homework Statement

Show that the free energy, F=SUM(E_i*p_i)+T*SUM(p_i*ln(p_i)) is minimal when p_i=e^(-E_i/T)/SUM(e^(-E_i/T))

Where E is energy, T is temperature

Nothing really

## The Attempt at a Solution

So if I just try and find the derivative of the force I arrive at something along the lines of p_i=e^((-E_i/T)-1).
I'm assuming I'm supposed to use some constraints to show that the entropy is fixed but I'm not sure how to go about doing that.