Factorization first, then finding each root, also known as "eye of a needle". After adjusting each factor to descending order, pay attention to the fact that the first coefficient of each factor should become a positive number, starting from the upper right of the number axis, and passing through the "eye of a needle" according to the law of "odd piercing even not piercing"! !

At infinity on the right side of the number axis, the value of x is infinite, and of course the algebraic value is positive.

Then cross a point to the left, then the value of one factor will be negative and the others will be positive, because the value of X in this interval is greater than all the roots of the left ratio and only less than the roots of the right ratio, so the value of the algebraic formula is negative.