WAEC 2018 Mathematics · Question 38
The graph of y = x and y = x intersect at which of these points?
Options
- A.(0,0), (1,1)
- B.(0,0), (0,1)
- C.(1, 0), (0, 0)
- D.(0, 0) (0, 0)
Answer: A. (0,0), (1,1)
Explanation written with AI and checked against the answer key
Analyze the question: We need the points where the curve y = x² meets the line y = x. At an intersection point, both equations give the same y-value, so we set them equal.
Concept: To find where two graphs intersect, equate the two expressions for y, solve for x, then substitute back to find y.
Solution:
- Set the equations equal: x² = x
- Rearrange: x² − x = 0
- Factorise: x(x − 1) = 0
- Solve: x = 0 or x = 1
- Find y using y = x: • When x = 0, y = 0, giving (0, 0) • When x = 1, y = 1, giving (1, 1)
Check: For (1, 1): y = x² gives 1² = 1 ✓ and y = x gives 1 ✓. For (0, 0): both give 0 ✓.
Checking the other options:
- B. (0, 1) is not on y = x, so it is wrong.
- C. (1, 0) is not on y = x, so it is wrong.
- D. This lists only (0, 0) twice, so it misses the second intersection point.
Answer: A. (0,0), (1,1)
Tip: Whenever you're asked for the intersection of two graphs, equate the two equations and solve. Never divide both sides by x in x² = x, because you would lose the solution x = 0. Always factorise instead.
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