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Multi-Logarithms (Posted on 2004-12-08) Difficulty: 2 of 5
If log9(x) = log12(y) = log16(x+y), then find y/x.

  Submitted by SilverKnight    
Rating: 3.4000 (5 votes)
Solution: (Hide)
Let: a = log9(x) = log12(y) = log16(x+y)
Then,
16^a = x + y = 9^a + 12^a.
Completing the square, we get:
(3^a + 1/2(4^a))^2 = (5/4)(4^a)^2.
Therefore 3^a = (√5-1)/2)4^a.
Then y/x = 12^a/9^a = 4^a/3^a = 2/(√5-1) = (1+√5)/2

Comments: ( You must be logged in to post comments.)
  Subject Author Date
SolutionPuzzle Solution (Method III)K Sengupta2008-04-06 13:10:28
SolutionPuzzle Solution (Method II)K Sengupta2008-02-28 05:39:49
SolutionPuzzle SolutionK Sengupta2007-03-19 12:01:53
re(3): I thinkRichard2005-01-21 03:11:36
re(2): I thinkmatt2005-01-20 23:39:39
Questionre: I thinkCharlie2005-01-20 19:17:40
I thinkmatt2005-01-20 17:01:13
re: GeneralizationJer2004-12-09 17:31:15
Generalizationowl2004-12-09 17:07:29
SolutionsolutionCharlie2004-12-08 15:29:24
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