1, Planar Cartesian Coordinate System: Draw two mutually perpendicular number axes with coincident origin on the plane to form Planar Cartesian Coordinate System.

2. Rational number: a number consisting of integers and fractions. Include positive integer, 0, negative integer, positive fraction and negative fraction. Can be written as the ratio of two integers.

3. The absolute value means the distance between the point representing a certain number on the number axis and the origin.

4. additive commutative law: a+b= b+ a is added, the position of the addend is exchanged, and the sum is unchanged.

5. If there are brackets, do the operation in brackets first, and then follow the brackets, brackets and braces in turn.