JAMB 2011 Mathematics · Question 11
If log318 + log33 - log3x = 3, Find x.
Options
- A.1
- B.2
- C.o
- D.3
Answer: B. 2
Explanation written with AI and checked against the answer key
Analyze the question: We have log₃18 + log₃3 − log₃x = 3 and need to find x.
Concept: Log laws (same base):
- log a + log b = log(ab)
- log a − log b = log(a/b)
- log_b(N) = k means N = b^k
Solution:
- Combine the logs: log₃(18 × 3 / x) = 3 log₃(54/x) = 3
- Convert to index form: 54/x = 3³ = 27
- Solve for x: x = 54/27 = 2
Check: log₃18 + log₃3 − log₃2 = log₃(54/2) = log₃27 = 3 ✓
Answer: x = 2, which is option B.
Tip: When you see several logs with the same base, first combine them into a single log (add → multiply, subtract → divide), then switch to index form. Also remember that 3³ = 27, which is a common value in JAMB questions.
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