The first step of the needle-piercing method, also known as the "needle-piercing method based on the number axis" or "using the number axis", is to shift the terms of inequality to make the right side zero through many properties of inequality. (Note: Make sure that the coefficient before x is positive) For example, put x3-2x2-x+2 >; 0 to (x-2)(x- 1)(x+ 1)>0 Step 2: replace the unequal sign with an equal sign and solve all the roots. For example, the root of (x-2)(x- 1)(x+ 1)=0 is: x 1=2, x2= 1, x3=- 1 Step 3: From left to right on the number axis. For example:-1 1 2 Step 4: Draw a line through the roots: Draw a line from the upper right to the lower left of the rightmost root based on the number axis, and then go up through the second right heel and pass through each root one by one. Step 5: Observe the inequality. If the inequality is ">", take the range above the number axis and within the heel line; If the sign is not equal to "",take the range above the number axis and within the following line. Namely:-1