WAEC 2010 Mathematics · Question 29

c c x 0 2 4 6 y 1 2 3 4 . The table is for the relation y = mx + c where m and c are constants. What is the…

Question

x0246y1234\begin{array}{c|c} x & 0 & 2 & 4 & 6\\ \hline y & 1 & 2 & 3 & 4\end{array}. The table is for the relation y = mx + c where m and c are constants. What is the equation of the line described in the tablet?

  1. A.y = 2x
  2. B.y = x + 1
  3. C.y = x
  4. D.y = 12x+1\frac{1}{2}x + 1

Answer: D. y = 12x+1\frac{1}{2}x + 1

Explanation written with AI and checked against the answer key

Analyze the question: The table gives points on a straight line y = mx + c. We need to find m (gradient) and c (y-intercept).

Concept: For a line y = mx + c:

  • c is the value of y when x = 0
  • m = (change in y) ÷ (change in x)

Solution:

  1. When x = 0, y = 1, so c = 1.
  1. Gradient using the points (0, 1) and (2, 2): m = (2 − 1) ÷ (2 − 0) = 1/2
  1. So the equation is y = ½x + 1.

Check with the other points:

  • x = 4: y = ½(4) + 1 = 3 ✓
  • x = 6: y = ½(6) + 1 = 4 ✓

Eliminating the other options:

  • A. y = 2x gives y = 0 at x = 0, but the table says 1 ✗
  • B. y = x + 1 gives y = 3 at x = 2, but the table says 2 ✗
  • C. y = x gives y = 0 at x = 0 ✗

Tip: In a table question, always check x = 0 first. It gives you c immediately. Then use any other point to find m, and test the remaining points to confirm. Notice also that x goes up by 2 each time while y goes up by 1, so the gradient is 1/2.

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