The use of rectangular coordinate system is presented along with examples, questions and their solutions.
A rectangular coordinate system in a Plane is used to plot points having an x coordinate and a y coordinate. A vertical number line, also called the y-axis, and a horizontal number line, also called x-axis, intersecting at a right angle form a system of coordinates in a plane as shown in figure 1 below. The point of intersection of the x and y axes is called the origin of the system of coordinates.
The x and y axes split the plane into four quadrants as noted in the figure above.
The signs of the x and y coordinates of a given point, gives enough information to find the quadrant of that point without plotting it.
Example
Points A=(4,2) and C=(−4,3) are both located above the x axis because their y coordinates 2 and 3 are both positive. But point A is on the right of the y axis and hence in quadrant I because its x coordinate 4 is positive.
The x coordinate of C, which is −4, is negative and therefore point C is to the left of the y axis, hence located in quadrant II.
Similar remarks could be made about points E=(−4,−2) in quadrant III and G=(4,−2) in quadrant IV.
Conclusion
Given a point with coordinates x and y, and without plotting the point, we can find the quadrant where the point will be located from the signs of x and y.
If x>0 and y>0, the point is in quadrant I
If x<0 and y>0, the point is in quadrant II
If x<0 and y<0, the point is in quadrant III
If x>0 and y<0, the point is in quadrant IV
Any point whose x coordinate is equal to zero, is located in the y axis because its distance from the y axis is equal to zero.
Example
Points A=(0,3), D=(0,−2) and E=(0,−4) all have the x coordinate equal to zero and are therefore located in the y axis. (see figure 4 below)
Any point whose y coordinate is equal to zero, is located in the x axis because its distance from the x axis is equal to zero.
Example
Points G=(6,0), C=(−2,0) and B=(−8,0) all have the y coordinate equal to zero and are therefore located in the x axis. (see figure 4 below)
A=(0,1), B=(2,0), C=(1,3), D=(−1,−1), E=(1,−3), F=(−3,1), G=(0,−4), H=(−3,0)
A=(−32,−89) in quadrant III
B=(0,45) on the y axis, above the x axis
C=(−88,0) on the x axis, to the left the y axis
D=(57,89) in quadrant I
E=(0,−77) on the y axis, below the x axis
F=(45,−38) in quadrant IV
G=(49,0) on the x axis, to the right the y axis
H=(−90,−56) in quadrant III
Group 1: A=(2,2),B=(−4,2),C=(−4,−1),D=(2,−1)
The four given points form a rectangle as shown below.
Group 2: A=(1,2),B=(−2,2),C=(−5,−2),D=(5,−2)
The four given points form a trapezoid as shown below.
Group 3: A=(0,4),B=(−2,2),C=(0,−4),D=(2,2)
The four given points form a kite as shown below.
plotting points in rectangular coordinate system
Geometry Tutorials and Problems
The Four Pillars of Geometry - John Stillwell - Springer; 2005th edition (Aug. 9 2005) - ISBN-10 : 0387255303
Geometry: A Comprehensive Course - Daniel Pedoe - Dover Publications - 2013 - ISBN: 9780486131733
Geometry: with Geometry Explorer - Michael Hvidsten - McGraw Hill - 2006 - ISBN: 0-07-294863-9