Question

Difficulty: EasyCoordinate Geometry of Straight Lines

What is the gradient of a line that is perpendicular to the line passing through the points (2,5)(2, 5) and (4,11)(4, 11)?

  1. A
    33
  2. −13-\frac{1}{3}Answer
  3. C
    13\frac{1}{3}
  4. D
    −3-3

Answer

The gradient of the perpendicular line is −13-\frac{1}{3}.
The gradient of the line connecting (2,5)(2, 5) and (4,11)(4, 11) is m=11−54−2=3m = \frac{11-5}{4-2} = 3. The gradient of a line perpendicular to it must satisfy m1⋅m2=−1m_1 \cdot m_2 = -1, yielding −13-\frac{1}{3}.

Step-by-Step Solution

1
Calculate the gradient m1m_1 of the line passing through (2,5)(2, 5) and (4,11)(4, 11).
m1=11−54−2=62=3m_1 = \frac{11 - 5}{4 - 2} = \frac{6}{2} = 3
The gradient formula between two points (x1,y1)(x_1, y_1) and (x2,y2)(x_2, y_2) is m=y2−y1x2−x1m = \frac{y_2 - y_1}{x_2 - x_1}.
2
Apply the condition for perpendicular lines to find the required gradient m2m_2.
m2=−1m1=−13m_2 = -\frac{1}{m_1} = -\frac{1}{3}
Two non-vertical lines are perpendicular if and only if the product of their gradients is −1-1 (m1⋅m2=−1m_1 \cdot m_2 = -1).

Key Concept

Perpendicular Line Gradients
Rate this question