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=11542=3m = \frac{11-5}{4-2} = 3. The gradient of a line perpendicular to it must satisfy m1m2=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=11542=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=y2y1x2x1m = \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 (m1m2=1m_1 \cdot m_2 = -1).

Key Concept

Perpendicular Line Gradients
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