If a line joining two points is horizontal, the slope is:

If a line joining two points is horizontal, the slope is:

• A. Undefined or no slope
• B. Positive
• C. Zero
• D. Negative

Answer: (C)

Slope tells you how much a line rises or falls as you move to the right. For a horizontal line, there’s no vertical change at all as you move along it, so the change in y is zero. Since slope is rise over run (Δy/Δx) and Δy = 0 while Δx ≠ 0, the slope is 0. This is different from a vertical line, which has undefined slope because the run is zero. A line that climbs has a positive slope, and one that falls has a negative slope, but a horizontal line has zero slope.

Slope tells you how much a line rises or falls as you move to the right. For a horizontal line, there’s no vertical change at all as you move along it, so the change in y is zero. Since slope is rise over run (Δy/Δx) and Δy = 0 while Δx ≠ 0, the slope is 0. This is different from a vertical line, which has undefined slope because the run is zero. A line that climbs has a positive slope, and one that falls has a negative slope, but a horizontal line has zero slope.