JAMB 2017 Mathematics · Question 35
What is the product of 2x2 − x + 1 and 3 − 2x
Options
- A.4x3 − 8x2 + 5x + 3
- B.−4x3 + 8x2 − 5x + 3
- C.−4x3 − 8x2 + 5x + 3
- D.4x3 + 8x2 − 5x + 3
Answer: B. −4x3 + 8x2 − 5x + 3
Explanation written with AI and checked against the answer key
Analyze the question: We need to multiply the polynomial (2x² − x + 1) by (3 − 2x). Each term in the first bracket must be multiplied by each term in the second.
Concept: Use the distributive law: (a + b + c)(d + e) = ad + ae + bd + be + cd + ce. Then collect like terms.
Solution:
Multiply each term of (2x² − x + 1) by 3:
- 2x² × 3 = 6x²
- −x × 3 = −3x
- 1 × 3 = 3
Multiply each term of (2x² − x + 1) by −2x:
- 2x² × (−2x) = −4x³
- −x × (−2x) = +2x²
- 1 × (−2x) = −2x
Add everything together:
−4x³ + (6x² + 2x²) + (−3x − 2x) + 3
= −4x³ + 8x² − 5x + 3
Check with x = 1: (2 − 1 + 1)(3 − 2) = 2 × 1 = 2 Option B: −4 + 8 − 5 + 3 = 2 ✓
(Option A gives 4 − 8 + 5 + 3 = 4, which fails, so it is wrong.)
Answer: The product is −4x³ + 8x² − 5x + 3, which is option B.
Tip: When an expression has a negative term like (3 − 2x), watch your signs carefully. A quick way to check on exam day is to substitute x = 1 into the question and into each option. It takes only a few seconds and eliminates wrong options fast.
AI can make mistakes. Report anything that looks wrong.
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