x-Coordinate — Definition, Formula & Examples
The x-coordinate is the first number in an ordered pair that tells you how far left or right a point is from the origin on a coordinate plane. A positive x-coordinate means the point is to the right of the origin, and a negative x-coordinate means it is to the left.
Given an ordered pair representing a point in the Cartesian plane, the x-coordinate is the signed horizontal distance from the y-axis to the point, measured along a line parallel to the x-axis. It is also called the abscissa.
How It Works
When you see a point written as , the x-coordinate is the first number: . To locate the point, start at the origin and move units to the right along the x-axis. Then move units up (that's the y-coordinate). If the x-coordinate were , you would move units to the left instead.
Worked Example
Problem: Identify the x-coordinate of the point and describe what it tells you about the point's position.
Step 1: Look at the ordered pair and find the first number.
Step 2: Interpret the sign. Since is negative, the point is 4 units to the left of the origin along the horizontal axis.
Answer: The x-coordinate is , meaning the point lies 4 units to the left of the y-axis.
Why It Matters
Reading x-coordinates correctly is essential for plotting points, graphing equations, and solving geometry problems on the coordinate plane. In courses from pre-algebra through calculus, nearly every graph you encounter depends on correctly identifying horizontal position from an ordered pair.
Common Mistakes
Mistake: Mixing up the x-coordinate and y-coordinate by reading the second number first.
Correction: Remember that in an ordered pair , the x-coordinate always comes first. Think alphabetical order: x before y.