Is addition associative so we don't need brackets

Question

Is ($a-b)+(c-b)=-2b+a+c$ ?

So if I have the following operation

$$\dot{x_1}(t) =\sum_{i=1}^{n}{(x_i - x_1)}$$

Can I write

$$\dot{x_1}(t) =- nx_1 +\sum_{i=1}^{n}(x_i)$$