Hello, everyone:

The number axis is such a straight line that defines a unique origin, a unique positive direction and a unique unit length.

First, let's introduce how to make the number axis: draw a horizontal straight line, take a point on the straight line to represent 0, this point is called the origin, and choose a certain length to get a number axis. All rational numbers can be represented by points on the number axis. As a unit length, the right direction of a straight line is defined as the positive direction. Starting from the origin, the positive point on the ray corresponds to a positive number, the negative point on the ray corresponds to a negative number, and the origin corresponds to zero.

Remind everyone that the number axis is a specific geometric figure; Origin, positive direction and length unit are the three elements of the shaft, and they are all indispensable.

The number axis is very useful: you can use the number axis to compare the sizes of two real numbers, the left is small and the right is large. Any rational number can be represented by a point on the number axis. But not all the numbers on the number axis are rational numbers. For example, you can use compasses to intercept numbers like the root number two.

Speaking of absolute value, it is also closely related to the number axis. Because any distance from the origin is its absolute value. If you can't imagine the absolute value, just look at the number axis. Similarly, the distance between two numbers on the number axis can also be expressed as the absolute value of the difference between the two numbers. Please note that the absolute value of any number is non-negative because the distance is non-negative.

In a word, the number axis is very useful, and it helps students a lot. Sometimes when I do inequality problems, I will draw a number axis, mark numbers and add symbols, and the problem will be solved.

Thank you. . .

Ah ah, I made up so much, you can change it yourself.

Give me the music. I've tried very hard.

thank you