Here is a differential equation that we are going to solve by separation of variables.
First we rewrite the equation in the differential form: h(y)dy=g(x)dx
Now we integrate both sides of the equation.
Remember the + C. However . . .
. . . there is no need to write + C on the left side because it can be subtracted from + C on the right side. By subtracting an arbitrary constant from another arbitrary constant, you get + C
Finally, we have the answer.