NECO 2002 Mathematics · Question 13
A quadratic equation with roots -1 and is
Options
- A.x2 + 3x + 4 = 0
- B.8x2 + 10x + 3 = 0
- C.8x2 +12x – 3 = 0
- D.8x2 + 10x-3.= 0
- E.8x2 + 12x + 3 = 0
Answer: D. 8x2 + 10x-3.= 0
Explanation written with AI and checked against the answer key
Analyze the question: We need a quadratic equation whose roots are -1½ (that is, -3/2) and 1/4.
Concept: If the roots are α and β, the equation is x² − (α + β)x + αβ = 0
Solution:
Sum of roots: -3/2 + 1/4 = -6/4 + 1/4 = -5/4
Product of roots: (-3/2)(1/4) = -3/8
Substitute into the formula: x² − (−5/4)x + (−3/8) = 0 x² + (5/4)x − 3/8 = 0
Multiply through by 8 to clear the fractions: 8x² + 10x − 3 = 0
Check with the options:
- Option B: 8x² + 10x + 3 = 0. The constant is +3, which is wrong.
- Option C: 8x² + 12x − 3 = 0. The middle term is wrong.
- Option D: 8x² + 10x − 3 = 0. This matches our result.
Quick verification: Put x = 1/4 into 8x² + 10x − 3: 8(1/16) + 10/4 − 3 = 0.5 + 2.5 − 3 = 0 ✓
Correct answer: D
Tip: Always use the pattern x² − (sum)x + (product) = 0. Watch the signs carefully: a negative sum becomes a positive middle term. Then multiply by the LCM of the denominators to get whole-number coefficients. Also, plugging one root back in is a quick way to confirm your answer.
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