Results 1 to 5 of 5

Math Help - Index form with a prime number base?

  1. #1
    Newbie
    Joined
    Jul 2010
    Posts
    3

    Index form with a prime number base?

    Hi, I desperately need help in knowing how to solve a problem that requires a number to be written in index form with a prime number base. I can see the answers in the back of the text, but I have no idea how they get those answers. This is for both whole numbers and fractions.

    An example of the questions are;

    1. 81
    2. 1/13
    Your help is greatly appreciated!
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Grand Panjandrum
    Joined
    Nov 2005
    From
    someplace
    Posts
    14,972
    Thanks
    4
    Quote Originally Posted by Trillian View Post
    Hi, I desperately need help in knowing how to solve a problem that requires a number to be written in index form with a prime number base. I can see the answers in the back of the text, but I have no idea how they get those answers. This is for both whole numbers and fractions.

    An example of the questions are;

    1. 81
    2. 1/13
    Your help is greatly appreciated!
    No, I think you will have to provide more context than that (form what you have posted I have no idea what your question is about)

    81=3^4, 1/13=13^{-1}

    CB
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Jul 2010
    Posts
    3
    Sorry, I didn't have much more to include. This is how it appeared in our textbook;

    2 Write each number in index form with a prime number base
    a) 8
    b) 64
    c) 81
    d) 32
    e) 625

    3 Write each number in index form with a prime number base
    a) 1/13
    b) 1/49
    c) 1/13^3
    d) 1/1024
    e) 9/729


    There was nothing else to show how you are meant to work it out or anything. There were examples given at the start of the chapter, but they gave the question and then they answered it in the solution, but they didn't demonstrate the method for working it out. A extensive google search showed factor trees, but again there was nothing showing how to apply a method to work out which numbers you needed because for larger numbers there are several prime numbers that could be used if that makes sense.
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Senior Member eumyang's Avatar
    Joined
    Jan 2010
    Posts
    278
    Thanks
    1
    I personally don't use any method per se in doing these. Maybe for me, I've worked with numbers long enough and I have a good enough memory to figure these out in my head.

    For instance (I'll show parts a and e of each)...

    2a) 8 = 2 \cdot 2 \cdot 2 = 2^3
    2e) 625 = 5 \cdot 5 \cdot 5 \cdot 5 = 5^4
    3a) \frac{1}{13} = 13^{-1}
    3e) \frac{9}{729} = \frac{1}{81} = \frac{1}{3 \cdot 3 \cdot 3 \cdot 3} = \frac{1}{3^4} = 3^{-4}

    Otherwise, factor trees may work. Here's an example showing that 625 = 5 x 5 x 5 x 5:
    Index form with a prime number base?-factortree.jpg
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Newbie
    Joined
    Jul 2010
    Posts
    3
    Thank you very much for that. that makes it a bit easier to understand.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. [SOLVED] prime index
    Posted in the Advanced Algebra Forum
    Replies: 1
    Last Post: December 2nd 2011, 06:16 PM
  2. Replies: 1
    Last Post: August 9th 2011, 03:04 PM
  3. Replies: 2
    Last Post: April 24th 2010, 07:38 PM
  4. Replies: 1
    Last Post: September 7th 2008, 07:47 AM
  5. Prime number of a form
    Posted in the Number Theory Forum
    Replies: 1
    Last Post: September 26th 2006, 07:36 PM

Search Tags


/mathhelpforum @mathhelpforum