Simplify it to the simplest factor, remove the part that is always greater than zero, and if there are odd coefficients before x that are less than zero, start from the bottom right.

In fact, you can change all the coefficients of the left X to be greater than zero, and draw a line from right to left and from top to bottom. If the original coefficient on the left is less than zero, sign the corresponding inequality. ("Left" refers to the left side of the inequality sign)