Results 1 to 2 of 2

Math Help - so confusing!

  1. #1
    Newbie
    Joined
    Oct 2006
    Posts
    7

    so confusing!

    hello! I am new! I can post any math homework question I have right?
    if this is the case I have one that I don't understand at all!
    determine two geometreic sequences whose first terms are 18x-9, 2x+8 and x-1 how would I go about and do this question?

    thanks for your help! in advance!
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Forum Admin topsquark's Avatar
    Joined
    Jan 2006
    From
    Wellsville, NY
    Posts
    9,668
    Thanks
    298
    Awards
    1
    Quote Originally Posted by george93 View Post
    hello! I am new! I can post any math homework question I have right?
    if this is the case I have one that I don't understand at all!
    determine two geometreic sequences whose first terms are 18x-9, 2x+8 and x-1 how would I go about and do this question?

    thanks for your help! in advance!
    I presume you are looking for two values of x that would suit?

    a_0 = a_0r^0 = 18x-9 <-- This defines a_0.

    a_1 = a_0r^1 = (18x-9)r = 2x+8 <-- This defines r.

    So r = \frac{2x+8}{18x-9}

    a_2 = a_0r^2 = (18x-9) \left ( \frac{2x+8}{18x-9} \right ) ^2 = \frac{(2x+8)^2}{18x-9} = x - 1 <-- This defines x.

    So solve for x:
    \frac{(2x+8)^2}{18x-9} = x - 1

    (2x+8)^2 = (18x-9)(x-1)

    4x^2 + 32x + 64 = 18x^2 - 27x + 9

    0 = 14x^2 - 59x - 55

    Frankly I wouldn't try to fiddle with factoring it, I'd just use the quadratic formula, but as it happens it DOES factor: (which I figured out by using the qf. )
    (14x + 11)(x - 5) = 0

    So x = 5 or x = -11/14.

    So your two sequences are:
    x = 5: 81, 18, 4, ...
    x = -11/14: -324/14, 90/7, -25/14, ...

    -Dan
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. a bit confusing
    Posted in the Statistics Forum
    Replies: 2
    Last Post: April 13th 2010, 06:28 PM
  2. Please Help me with my HW! SOO confusing
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: September 5th 2009, 09:22 PM
  3. confusing >.<
    Posted in the Algebra Forum
    Replies: 4
    Last Post: June 20th 2009, 09:28 PM
  4. very confusing!
    Posted in the Algebra Forum
    Replies: 4
    Last Post: March 31st 2009, 08:42 AM
  5. Help! This is confusing!
    Posted in the Algebra Forum
    Replies: 3
    Last Post: January 25th 2007, 04:16 PM

Search Tags


/mathhelpforum @mathhelpforum