Need help on Math Hmwk !~~

• VagueHart

  27 Jan 07, 00:06

  Sorry my math veh poor one..
  
  Lets use * to denote the power of
  EG 2*2 = 4 okk??
  
  How to do the below question?
  
  Solve the equation below giving your answers corrected to 3 significant figures
  2lg(3x-2) = 5lg2.7
  
  Izzit a quadratic equation in the end?
  
  I do untill 9x*2-12x-139 = 0 den cannot do liao since 139 can only be formed by itself... >.<
  
  Thanks in advance !~
• the Bear

  27 Jan 07, 00:11

  uhh.. 5lg2.7 = lg(2.7)*5 = some very huge number with 5 decimal places right?
  
  

  Originally posted by VagueHart:

  Sorry my math veh poor one..
  
  Lets use * to denote the power of
  EG 2*2 = 4 okk??
  
  How to do the below question?
  
  Solve the equation below giving your answers corrected to 3 significant figures
  2lg(3x-2) = 5lg2.7
  
  Izzit a quadratic equation in the end?
  
  I do untill 9x*2-12x-139 = 0 den cannot do liao since 139 can only be formed by itself... >.<
  
  Thanks in advance !~

• VagueHart

  27 Jan 07, 00:16

  err my calculator spoil so I use the microsoft one... I first type 2.7*5 which is 143.489 den lg it.. I got 2.1568
• the Bear

  27 Jan 07, 00:18

  why lg it?
  
  remove the external multiplier on both sides so you get lg a = lg b
  
  therefore a = b
  
  then solve it using the formula for quadratic equations
• VagueHart

  27 Jan 07, 00:21

  Did that, i got the quad equation... its 9x*2-12x-139 which I think is impossible to do ask 139 is a number that can be divided only by itself and 1
• Lorry`

  27 Jan 07, 00:22

  i think he's sayin the end equation is 9x^2 - 12x - 139 = 0
  and since 139 = 1* 139 only, then cannot solve, cant use cross method
  
  hmm.. sec3 maths if i can rem ?
  theres another method to solve? other than cross method,
  maybe try the -b plusminus squareroot b^2 - 4ac over 2a method ?
• VagueHart

  27 Jan 07, 00:25

  oh ya... ok i go try now.. thanks
• the Bear

  27 Jan 07, 00:26

  point: never lower it to 3 sig fig in the course of your calculations...
  
  which means you have to get the whole mess of 5 decimal places until the last bit..
  
  so you use this:
  
  
  
  to solve..
  
  

  Originally posted by VagueHart:

  Did that, i got the quad equation... its 9x*2-12x-139 which I think is impossible to do ask 139 is a number that can be divided only by itself and 1

• hisoka

  27 Jan 07, 00:29

  2lg(3x-2) = 5lg(2.7)
  
  =>lg(3x-2) = lg((2.7)^(5/2))
  therefore, 3x-2 = 2.y^(5/2)
• Lorry`

  27 Jan 07, 00:32

  actually i was wonderin, can straight away round off to a whole number meh?
  9x^2 - 12x = 139.48907
  
  the bear is right, should use the 139.48907 first, more accurate
• seow

  27 Jan 07, 00:33

  so free can teach math cannot go sbh crapbox.
• VagueHart

  27 Jan 07, 00:34

  
  
  hehe thanks guys!~ done it thanks alot!
• Lorry`

  27 Jan 07, 00:37

  hisoka's method also can be used, it's faster, but in terms of accuracy im not sure which's better
  
  
• the Bear

  27 Jan 07, 00:40

  it's almost the same for the basic level...
  
  you kind of lose a pile of stuff like complex numbers because lg(-ve number) isn't on the natural number line or something like that
  
  

  Originally posted by Lorry`:

  hisoka's method also can be used, it's faster, but in terms of accuracy im not sure which's better
  
  

• VagueHart

  27 Jan 07, 00:41

  why hisoka's method got y de?? typo?? sorry my math really veh terrible de
• the Bear

  27 Jan 07, 00:42

  type wrongly.. notice y is near 7
  
  should be 2.7
  
  

  Originally posted by VagueHart:

  why hisoka's method got y de?? typo?? sorry my math really veh terrible de

• hisoka

  27 Jan 07, 00:43

  Originally posted by VagueHart:

  why hisoka's method got y de?? typo?? sorry my math really veh terrible de

  2.7 sorry typo, the metohd mroe important lah
• SGpork

  27 Jan 07, 00:44

  wa this is getting famous
  
  everyone post their hmw
  
  
• Lorry`

  27 Jan 07, 00:47

  Originally posted by the Bear:

  it's almost the same for the basic level...
  
  you kind of lose a pile of stuff like complex numbers because lg(-ve number) isn't on the natural number line or something like that
  
  

  hmm.... ok
  are you a maths teacher?
• the Bear

  27 Jan 07, 00:48

  nope.. last time i did math homework was in JC.. which is more than half a lifetime ago
  
  

  Originally posted by Lorry`:

  hmm.... ok
  are you a maths teacher?

• gLc

  27 Jan 07, 08:23

  Originally posted by Lorry`:

  i think he's sayin the end equation is 9x^2 - 12x - 139 = 0
  and since 139 = 1* 139 only, then cannot solve, cant use cross method
  
  hmm.. sec3 maths if i can rem ?
  theres another method to solve? other than cross method,
  maybe try the -b plusminus squareroot b^2 - 4ac over 2a method ?

  sec3 meh?
  
  I sec4 now and i dont even understand the question...
• LinkageII

  27 Jan 07, 08:30

  Originally posted by gLc:

  sec3 meh?
  
  I sec4 now and i dont even understand the question...

  ya.. logarithm's sec 3 work
• dahliamorie

  27 Jan 07, 10:37

  we should have a homework forum man. since so many ppl asking for help for their homeworks.
• davidche

  27 Jan 07, 13:21

  i am sec 3 but i dont know wtm is lg.
  
  use the fomula: x= (-b +/-square root b*2 - 4(a)(c)) over 2(a)