WAEC 2013 Mathematics · Question 45
Given that = , make q the subject of the equation
Options
- A.q = p
- B.q = p3r
- C.q = pr3
- D.q = pr
Answer: C. q = pr3
Explanation written with AI and checked against the answer key
Analyze the question: We are given p^(1/3) = (∛q)/r and must make q the subject.
Concept: To remove a cube root, cube both sides. Remember (a^(1/3))³ = a and (∛q)³ = q.
Solution:
- Start with: p^(1/3) = ∛q / r
- Multiply both sides by r: r·p^(1/3) = ∛q
- Cube both sides: (r·p^(1/3))³ = q
- Simplify: r³ · p = q
So q = pr³
Check: Take p = 8 and r = 2. Then p^(1/3) = 2, so ∛q / 2 = 2, which gives ∛q = 4 and q = 64. Using the formula: pr³ = 8 × 8 = 64 ✓.
Matching the options: The options appear to have lost their formatting. Option C, "pr3", is read as pr³, which matches our result. Option B, "p3r", would read as 3pr, which does not match.
Exam tip: When a variable sits inside a root, isolate the root first, then raise both sides to the power that cancels it (cube for a cube root, square for a square root). Also, when cubing a product, cube each factor: (r·p^(1/3))³ = r³·p.
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