8/26/2014 If three numbers log a, log b, log c from an arithmetic progression (in that order), which of the following is true?

a) b = ac

b) c = ab

c) b = (a + c)/2

d) b² = ac

e) b² = a + c

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8/26/2014 Solution. D. Since log a, log b, log c from an arithmetic progression, log b – log a = log c – log b [since they form the same common difference], so that log (b / a) = log (c /b) → b² = ac after canceling the log and cross-multiplying.