What is the meaning of "odd through even" in the ordinal axis root method?

First step: through the many properties of inequality on the inequality to shift the term, so that the right side of 0. (Note: must ensure that the coefficients before x is positive) For example: x ^ 3 - 2x ^ 2 - x + 2 & gt; 0 to (x - 2) (x - 1) (x + 1) & gt; 0 The second step: the inequality sign into an equal sign to solve for all the roots. For example, the roots of (x-2)(x-1)(x+1)=0 are: x1=2, x2=1, x3=-1 Step 3: Label the roots from left to right on the number axis. For example: -1 1 2 Step 3: Draw a line through the roots: using the number axis as a standard, cross the roots from the upper right of the "rightmost root", draw a line down to the left, and then cross the "second right heel" up, up and down through the roots in turn. Step 4: Observe the inequality sign, if the inequality sign is "& gt;", then take the top of the number axis, through the range of the heel line; if the inequality sign is "& lt;" then take the bottom of the number axis, through the range of the heel line. Example: To find the roots of (x-2)(x-1)(x+1)>0. Labeling the roots on the number axis yields: -1 1 2 Drawing the root-piercing line: start at the top right and pierce the roots. Since the inequality sign is ">" then take the range above the number axis, within the line through the heel. That is: -1 & lt; x & lt; 1 or x & gt; 2. The so-called "odd over even but" is not only odd or even, but refers to each of the causes of the phase of the median If the median is odd, then it is odd median is even, then it is even, and does not mean that the root