Advanced MathHardCounting intersections of a line and a parabola
Advanced Math practice question
In the xy-plane, how many points do the graphs of y = x² + 1 and y = x have in common?
- A. ZeroCorrect
- B. Exactly one
- C. Exactly two
- D. Infinitely many
Answer: A. Zero
Set them equal: x² + 1 = x, so x² − x + 1 = 0. The discriminant is (−1)² − 4(1)(1) = −3, which is negative, so there are no real solutions — the graphs never meet. (The parabola's lowest point is (0, 1), which already sits above the line there.)
Why the other answers are wrong
- B. Exactly one
- Exactly one point would need a discriminant of zero; here it's −3.
- C. Exactly two
- Two points would need a positive discriminant. −3 is negative.
- D. Infinitely many
- A line and a parabola can share at most two points; infinitely many is impossible.
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