Draw two number axes perpendicular to each other and having a common origin on a two-dimensional plane, which is called rectangular coordinate system for short. The plane rectangular coordinate system has two coordinate axes, in which the horizontal axis is the X axis and the right direction is the positive direction; The vertical axis is the y axis and the direction is the positive direction. The plane where the coordinate system is located is called the coordinate plane, and the common origin of the two coordinate axes is called the origin of the plane rectangular coordinate system. X axis and Y axis divide the coordinate plane into four quadrants, the upper right part is called the first quadrant, and the other three parts are called the second quadrant, the third quadrant and the fourth quadrant in turn counterclockwise. Quadrants are bounded by the number axis, and the points and origins on the horizontal and vertical axes are not in any quadrant. In general, the X axis and the Y axis take the same unit length, but under special circumstances, they can also take different unit lengths.

quadrant

The first quadrant can also be written as I, the second quadrant as II, the third quadrant as III and the fourth quadrant as IV.

The horizontal and vertical coordinates of the points on the bisector of the first quadrant and the third quadrant are equal; The horizontal and vertical coordinates of the points on the bisector of the second and fourth quadrants are opposite to each other.

symmetry point

1. Regarding the coordinates of the axisymmetrical points on the X axis, the abscissa is the same and the ordinate is opposite. (horizontal and vertical)

2. With regard to the coordinates of points symmetrical about the Y axis, the ordinate is the same, and the abscissa is opposite. (horizontal and vertical)

3. With regard to the coordinates of a point whose origin center is symmetrical, the abscissa and abscissa are reciprocal, and the ordinate and ordinate are reciprocal. (Horizontal and vertical directions)

Symbol of point

Abscissa and ordinate

The first quadrant: (+,+) is positive.

The second quadrant: (-,+) negative and positive

The third quadrant: (-,-) negative.

The fourth quadrant: (+,-) plus or minus

Positive semi-axis of X axis: (+,0)

X-axis negative half axis: (-,0)

Positive semi-axis of Y axis: (0,+)

Negative semi-axis of Y axis: (0,-)

See Baidu entry:

Plane rectangular coordinate system? /view/7 1628.htm

Cartesian coordinate system? /view/968758.htm