WAEC 2014 Mathematics · Question 48

Find the gradient of the line joining the points (2, -3) and 2, 5)

Options

  1. A.9
  2. B.1
  3. C.2
  4. D.undefined

Answer: D. undefined

Explanation written with AI and checked against the answer key

Analyze the question: We need the gradient (slope) of the line through (2, -3) and (2, 5). The second point is written as "2, 5)", which is a typo for (2, 5).

Concept: Gradient = (y₂ − y₁) / (x₂ − x₁)

Solution:

  • Point 1: (x₁, y₁) = (2, -3)
  • Point 2: (x₂, y₂) = (2, 5)

m = (5 − (−3)) / (2 − 2) = 8 / 0

Division by zero is not defined, so the gradient is undefined.

Why this makes sense: Both points have the same x-coordinate (x = 2), so the line is a vertical line. A vertical line has no run (horizontal change is 0), and its gradient is undefined.

Checking the other options:

  • A (9): not obtainable from any valid calculation here.
  • B (1) and C (2): these would need a nonzero denominator. For example, 8/4 = 2 would need different x-values.
  • D (undefined): matches our working.

Exam tip: Always compare the x-coordinates first.

  • Same x-values → vertical line → gradient undefined.
  • Same y-values → horizontal line → gradient 0.

This saves time and avoids careless errors.

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