How to do this two A Math logarithm questions?

• AmuletxHeart

  8 May 10, 22:22

  Express Y in terms of X.

• Forbiddensinner

  8 May 10, 23:52

  Originally posted by AmuletxHeart:

  Express Y in terms of X.

  This single statement is not going to allow us to help you ..... 

  You will need to give more information.

   

  Anyway....Shugo Chara? 

• LatecomerX

  8 May 10, 23:59

  Originally posted by AmuletxHeart:

  Express Y in terms of X.

  X   X
   X X
    X
    X
    X

   

• SBS261P

  9 May 10, 01:43

  Originally posted by LatecomerX:

  X   X
   X X
    X
    X
    X

   

  
  LOL =D

• AmuletxHeart

  9 May 10, 12:53

  Opps how to edit my original post? The scanned picture ain't showing up.

• AmuletxHeart

  9 May 10, 14:58

  Anyways heres the questions:

  [URL=http://img683.imageshack.us/i/30761118376673371918147.jpg/][IMG]http://img683.imageshack.us/img683/5356/30761118376673371918147.jpg[/IMG][/URL]

   

• ThunderFbolt

  9 May 10, 16:40

  these are actually rather standard questions. the thing to remember is that

  log_x (x) = 1 (meaning the log in base x working on x is 1)

  a log b = log b^a (meaning b to the power of a, like 3 to the power of 2 is 9)

  log x + log y = log xy

• AmuletxHeart

  9 May 10, 17:52

  

  Arg I hate the time limit between posts imposed on newbs.

  Anyway, here is where I'm stuck at question C.

  2 log_3 (y) - 4 = 3 log_3(x+2)

  log_3 y^2 - 4log _3 (3) = log_3 (x+2)^3

  log_3 y^2 - log_3(3^4) = log_3 (x+2)^3

   

  So how to remove the logs and make it just X and Y?

  Thanks.

• Forbiddensinner

  9 May 10, 18:38

  Originally posted by AmuletxHeart:

  

  Arg I hate the time limit between posts imposed on newbs.

  Anyway, here is where I'm stuck at question C.

  2 log_3 (y) - 4 = 3 log_3(x+2)

  log_3 y^2 - 4log _3 (3) = log_3 (x+2)^3

  log_3 y^2 - log_3(3^4) = log_3 (x+2)^3

   

  So how to remove the logs and make it just X and Y?

  Thanks.

  Remember that log a + log b = log ab and log a - log b = log a/b

  Hence, log(3) y^2 - log(3) 3^4 is the same as log (3) y^2/ 81

  Thus, log(3) y^2/ 81 = log(3) (x + 2)^3, and y^2/ 81 = (x + 2)^3

  y^2 = 81(x + 2)^3

  y = sqrt(81(x + 2)^3)

  y= 9sqrt(x + 2)^3 or y= -9sqrt(x + 2)^3

   

  Amu-chan. 

• ThunderFbolt

  9 May 10, 18:42

  From log x + log y = log xy

  Your working would continue to become

  log_3 ((y^2)/(3^4)) = log_3 ((x+2)^3)

  Which would allow you to remove logs from both sides to get

  (y^2)/(3^4) = (x+2)^3

  Where you can easily find y. 

  Remember that you can only remove them like this when both logs are in the same base and there is only 1 log term on each side. 

  And since y is squared, you may need your ± sign. 

  Edit: Beaten by 4 mins, ah well. =)

• Forbiddensinner

  9 May 10, 20:06

  Originally posted by ThunderFbolt:

  From log x + log y = log xy

  Your working would continue to become

  log_3 ((y^2)/(3^4)) = log_3 ((x+2)^3)

  Which would allow you to remove logs from both sides to get

  (y^2)/(3^4) = (x+2)^3

  Where you can easily find y. 

  Remember that you can only remove them like this when both logs are in the same base and there is only 1 log term on each side. 

  And since y is squared, you may need your ± sign. 

  Edit: Beaten by 4 mins, ah well. =)

  Nvm, it is the heart that matters. 

  Besides, this serves as double confirmation.

   

• Rooney9

  9 May 10, 20:11

  Originally posted by Forbiddensinner:

  Nvm, it is the heart that matters. 

  Besides, this serves as double confirmation.

   

  
  u r a math genius. btw double confirmation is redundant, just like repeat again.

  or reverse backwards.

• SBS261P

  9 May 10, 23:03

  Originally posted by Rooney9:

  
  u r a math genius. btw double confirmation is redundant, just like repeat again.

  or reverse backwards.

  
  ppl math pro only mah. haha just kidding.

  sometimes if you reuse the terms again and again (ahem this is also redundant) it might just stick! like "brokeback" which apparently has been included in the dictionary (",)