WAEC 2012 Mathematics · Question 23
Find the coefficient of m in the expression of () (m + )
Options
- A.-
- B.-
- C.-1
- D.-1
Answer: D. -1
Explanation written with AI and checked against the answer key
Analyze the question: We need to expand (m/2 − 1½)(m + 2/3) and find the coefficient of m, which is the number multiplying m after collecting like terms.
Concept: Use FOIL (First, Outer, Inner, Last) to expand, then combine the m terms.
Solution:
Write 1½ as 3/2, so the expression is (m/2 − 3/2)(m + 2/3).
- First: (m/2)(m) = m²/2
- Outer: (m/2)(2/3) = m/3
- Inner: (−3/2)(m) = −3m/2
- Last: (−3/2)(2/3) = −1
Collect the m terms:
m/3 − 3m/2 = (2m − 9m)/6 = −7m/6
−7/6 = −1 1/6
So the expansion is m²/2 − (7/6)m − 1, and the coefficient of m is −7/6 = −1 1/6.
Answer: Option D, −1 1/6.
Tip: Convert mixed numbers to improper fractions before multiplying (1½ = 3/2). Then use a common denominator when combining the m terms. Mixed numbers inside brackets are a common source of errors.
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