WAEC 2014 Mathematics · Question 48
Find the gradient of the line joining the points (2, -3) and 2, 5)
Options
- A.9
- B.1
- C.2
- 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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