Consider a mass $m$ with a spring on either end, each attached to a wall. The mass can freely move horizontally, without friction forces. Let $k_1$ and $k_2$ be the spring constants of the springs respectively with equilibrium position $x_1$ and $x_2$. Write a function for the equilibrium position $x_0$ of the system using $k_1$, $k_2$, $x_1$, $x_2$ and $m$.
Why can't we set the equilibrium position at $x_0=0$ since we are free to choose where the origin is?