12 Oct, 04:51AM in sunny Singapore!
Home → Homework Forum →

A maths sec 3

Subscribe to A maths sec 3 10 posts

Please Login or Signup to reply.
  • gobez14
    gobez14's Avatar
    1,364 posts since Apr '07
    • 19 Jan `08, 2:44PM

      hi

      can any1 tell mi wads teh answer of 3 log a (2) - 4 + log a (a to the power of 3) whe nconverted into a single logarithmic form

      and value of x when 4 (x to the power of half) = 3-7x

  • Moderator
    ^tamago^
    我又郁闷了...
    ^tamago^'s Avatar
    49,846 posts since Sep '03
    • 19 Jan `08, 3:04PM

      3 log(a,2) - 4 + log(a,a³)
      = log(a,8) - log(a,a^4) + log(a,a³)
      = log[a,(8/a)]

      4*sqrt(x)=3-7x
      Let z be sqrt(x), z>=0
      7z²+4z-3=0
      (7z-3)(z+1)=0
      z = 3/7 or -1 (rej. as z>=0)
      x = sqrt(3/7)

      Edited by ^tamago^ 19 Jan `08, 3:06PM
  • gobez14
    gobez14's Avatar
    1,364 posts since Apr '07
    • 19 Jan `08, 3:23PM
      Originally posted by ^tamago^:
      3 log(a,2) - 4 + log(a,a³)
      = log(a,8) - log(a,a^4) + log(a,a³)
      = log[a,(8/a)]

      4*sqrt(x)=3-7x
      Let z be sqrt(x), z>=0
      7z²+4z-3=0
      (7z-3)(z+1)=0
      z = 3/7 or -1 (rej. as z>=0)
      x = sqrt(3/7)

      how come liddat ar? 7z²+4z-3=0

  • SBS261P
    SBS261P's Avatar
    31 posts since Dec '07
  • Moderator
    ^tamago^
    我又郁闷了...
    ^tamago^'s Avatar
    49,846 posts since Sep '03
    • 19 Jan `08, 3:31PM
      Originally posted by gobez14:
      how come liddat ar? 7z²+4z-3=0

      sqrt(x) = z
      x = z²

      4*sqrt(x)=3-7x
      4z=3-7z²
      7z²+4z-3=0
      (7z-3)(z+1)=0
      z = 3/7 or -1

  • Moderator
    ^tamago^
    我又郁闷了...
    ^tamago^'s Avatar
    49,846 posts since Sep '03
    • 19 Jan `08, 3:32PM
      Originally posted by SBS261P:
      gt careless mistake... shld be

      z = 3/7

      x = (3/7)^2 = 9/49

      oh yeah. fug~!

  • gobez14
    gobez14's Avatar
    1,364 posts since Apr '07
    • 19 Jan `08, 3:45PM
      Originally posted by SBS261P:
      gt careless mistake... shld be

      z = 3/7

      x = (3/7)^2 = 9/49

      can elaborate?

  • wishboy
    wishboy's Avatar
    1,205 posts since Aug '05
    • 19 Jan `08, 8:02PM
      Originally posted by gobez14:
      can elaborate?

      4x^½ = 3 - 7x

      Let x^½ be u

      4u = 3 - 7u²
      7u² + 4u - 3 = 0
      (7u - 3)(u + 1) = 0
      7u - 3 = 0 or u + 1 = 0
      u = 3/7 or u = -1
      x^½ = 3/7 or x^½ = -1
      x = 9/49 or 1

      FYI, x^½ is equals to "square root of x", written as "sqrt x"

  • gobez14
    gobez14's Avatar
    1,364 posts since Apr '07
    • 20 Jan `08, 9:28AM
      Originally posted by wishboy:
      4x^½ = 3 - 7x

      Let x^½ be u

      4u = 3 - 7u²
      7u² + 4u - 3 = 0
      (7u - 3)(u + 1) = 0
      7u - 3 = 0 or u + 1 = 0
      u = 3/7 or u = -1
      x^½ = 3/7 or x^½ = -1
      x = 9/49 or 1

      FYI, x^½ is equals to "square root of x", written as "sqrt x"

      but hor y i sub 1 into the original equation 1 side is 4 the other side is -4 ?
      liddat still can??

  • SBS261P
    SBS261P's Avatar
    31 posts since Dec '07
    • 20 Jan `08, 10:50AM

      x cannot be 1 becoz

      x^1/2 = -1 means

      square root x = -1

      but square root cannot give negative number so must reject Very Happy

Please Login or Signup to reply.