Results 1 to 3 of 3

Math Help - Arithmetic and geometric sequence

  1. #1
    Member
    Joined
    Dec 2008
    Posts
    152

    Arithmetic and geometric sequence

    You have an arithmetic and geometric sequence. Both have 3 numbers in it. (ie. in arith. s. would be for example 2,4,6; in geo. s. would be 2,4,8

    The 3rd number in both sequences is 24.

    if you multiply the 1st number of arith. sequence and 1st number of geo. sequence you get 18.
    if you multiply the 2nd number of arith. sequence and 2nd number of geo. sequence you get 108.

    Write down both sequeneces..

    ----------------------------------
    I managed to get that far:

    a (letter which i use for arithm. sequences)
    b (letter for geo. sequences)
    (a1 = 1st number of the sequences... etc)

    a3 = a1 + 2d = 24 = b1 * k^2
    a1 * b1 = 18
    a2 * b2 = 108


    can someone please help..
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Moo
    Moo is offline
    A Cute Angle Moo's Avatar
    Joined
    Mar 2008
    From
    P(I'm here)=1/3, P(I'm there)=t+1/3
    Posts
    5,618
    Thanks
    6
    Hello,

    Quote Originally Posted by metlx View Post
    You have an arithmetic and geometric sequence. Both have 3 numbers in it. (ie. in arith. s. would be for example 2,4,6; in geo. s. would be 2,4,8

    The 3rd number in both sequences is 24.

    if you multiply the 1st number of arith. sequence and 1st number of geo. sequence you get 18.
    if you multiply the 2nd number of arith. sequence and 2nd number of geo. sequence you get 108.

    Write down both sequeneces..

    ----------------------------------
    I managed to get that far:

    a (letter which i use for arithm. sequences)
    b (letter for geo. sequences)
    (a1 = 1st number of the sequences... etc)

    a3 = a1 + 2d = 24 = b1 * k^2
    a1 * b1 = 18
    a2 * b2 = 108


    can someone please help..
    You've stated the equations correctly !

    Now, I'm sure it would help if you consider these two new equations :
    a_2=a_1+d
    b_2=b_1*k

    Follow Math Help Forum on Facebook and Google+

  3. #3
    Member
    Joined
    Dec 2008
    Posts
    152
    yea i know that, but i don't have k nor d..
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 1
    Last Post: December 3rd 2009, 12:35 PM
  2. Geometric and Arithmetic Sequence
    Posted in the Algebra Forum
    Replies: 2
    Last Post: January 9th 2009, 03:01 AM
  3. Replies: 2
    Last Post: January 23rd 2007, 09:47 AM
  4. Replies: 12
    Last Post: November 15th 2006, 01:51 PM
  5. geometric and arithmetic sequence
    Posted in the Algebra Forum
    Replies: 3
    Last Post: August 16th 2006, 01:50 PM

Search Tags


/mathhelpforum @mathhelpforum