Coordinates of Two Points

Date: 04/23/2002 at 23:21:25
From: Taylor
Subject: Seeing Things Graphically (Coordinates)

Dear Dr. Math, 

My teacher asked for the coordinates of two points that lie on the 
x-axis. I figured that all points on the x-axis must have an 
x-coordinate of 0, so I wrote (0,4) and (0,98). My friend says that 
points on the x-axis actually have a y-coordinate of 0. That sounds 
pretty silly to me. If my friend is right, why would they call it the 
x-axis?

Taylor

Date: 04/24/2002 at 08:56:15
From: Doctor Peterson
Subject: Re: Seeing Things Graphically (Coordinates)

Hi, Taylor.

The x-axis is the axis along which the x coordinate CHANGES, while 
the y coordinate stays zero.

     Y
     ^
     |     (x,y)
   y +----o
     |    |
     |    |
     +----+--->X
          x

We assign coordinates to points in the plane by choosing two 
perpendicular lines and labeling points along each axis with 
coordinates. The coordinates of any point are found by dropping 
perpendiculars from the point to the two axes; its x-coordinate is 
the location along the x-axis where the perpendicular meets. For any 
point on the x-axis, the perpendicular to the y-axis lands at the 
origin, so its y-coordinate is zero.

- Doctor Peterson, The Math Forum
  http://mathforum.org/dr.math/