How do you find the distance between two points on a coordinate plane with the same y-coordinate?

• A. By finding the absolute difference between their x-coordinates.
• B. By calculating the mean of x-coordinates.
• C. By multiplying coordinates.
• D. By adding the x-coordinates.

Answer: (A)

When two points share the same y-coordinate, you’re measuring a horizontal distance along that horizontal line. If the points are (x1, y) and (x2, y), the vertical difference is zero, so the distance between them is just how far apart their x-values are. That distance is the absolute value of the difference of the x-coordinates: |x2 − x1|. The absolute value is important because distance is always nonnegative, no matter which point you start from.

For example, points (3, 5) and (7, 5) are 4 units apart, since |7 − 3| = 4.

The other options don’t measure distance: averaging the x-coordinates gives a midpoint, not the distance; multiplying or adding the coordinates doesn’t describe how far apart the points are.