It is said that one day Descartes, a French philosopher and mathematician, was seriously ill in bed. Nevertheless, he repeatedly thought about a problem: geometric figures are intuitive, while algebraic equations are abstract. Can geometric figures be combined with algebraic equations, that is, can geometric figures be used to represent equations? In order to achieve this goal, the key is how to link the points that make up the geometric figure with each group of "numbers" that satisfy the equation. He thought hard and tried to figure out how to connect "point" with "number". Suddenly, he saw a spider in the corner of the roof and pulled down the silk. After a while, the spider climbed up along the silk, drawing left and right. The spider's "performance" made Descartes' thinking suddenly clear. He thought, you can think of a spider as a point. It can move up and down, left and right in the room. Can you determine every position of the spider with a set of numbers? He also thinks that two adjacent walls in the room pass three lines to the ground. If the angle on the ground is taken as the starting point and the three intersecting lines are taken as the three axes, then the position of any point in space can be used to find three numbers in turn. Conversely, a set of three ordered numbers can be given at will, and a corresponding point p can be found in the space. Similarly, a point on the plane can be represented by a set of numbers (x, y), and a point on the plane can also be represented by a set of two ordered numbers, which is the prototype of the coordinate system.