Calculate the value of x from log(324)/log(18) = log(x).
2023
Calculate the value of x from log(324)/log(18) = log(x).
- A.
10
- B.
100
- C.
0
- D.
45
Show answer & explanation
Correct answer: B
Concept
For a logarithm ratio log(a)/log(b), this equals logb(a) — the ratio's value is independent of which base is used for log itself, as long as the SAME base is used top and bottom. Also, the power rule states log(an) = n·log(a) for any base. Finally, by the definition of a logarithm, log(x) = k means x = (base)k.
Application
Recognize that 324 can be expressed as a power of 18: 18 × 18 = 324, i.e. 324 = 182.
Rewrite the numerator using the power rule: log(324) = log(182) = 2·log(18).
Substitute back into the ratio: log(324)/log(18) = 2·log(18)/log(18) = 2.
The original equation becomes log(x) = 2.
By the definition of a (base-10) logarithm, log(x) = 2 means x = 102 = 100.
Cross-check
Substituting x = 100 back: log(100) = log(102) = 2, which matches log(324)/log(18) = 2 computed above (numerically, log(324) ≈ 2.5105 and log(18) ≈ 1.2553, and their ratio ≈ 2). This confirms x = 100.