如何在直线上打破一个长方程?

I am trying to add an equation in a new line. The problem is that the equation is too long for the line, and I need to break it manually. Otherwise, it just overlaps to the right column, or to the right margins (and looks ugly...). Is there a way LaTeX can brake the equation for me, so it seems nice?I am trying to add an equation in a new line. T