Say you have an equation like this. Xcos17 + Xsin17 = 600 If I want to solve for X, I know that I can divide by cos17 + sin17. So it ends up being X = 600/(cos17 + sin17). However, why is it that it becomes just one X on the left side? There are two X's and dividing by cos17 + sin17 does not cancel the other X so why is it that only one X stays?