1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Help with a C1 level question

  1. Jan 3, 2007 #1
    Show that [​IMG] where k is a constant to be found.

    I know that a = 2 and that d = 1/2 and substituting these figires into Sn = (2a + (n-1) d) gives n/2 (4 + (n-1)/2) but I just can't see how to get from n/2 (4 + (n-1)/2) to the answer of 1/4n(n+7). I'd really appreciate it if someone could please explain.

    Thank you.

    Cathy
     
  2. jcsd
  3. Jan 3, 2007 #2

    AlephZero

    User Avatar
    Science Advisor
    Homework Helper

    Try using

    4 + (n-1)/2 = (8+n-1)/2 = (n+7)/2
     
  4. Jan 3, 2007 #3
    Thanks for replying but I still don't understand how you get from 4 + (n-1)/2 to (8+n-1)/2.
     
  5. Jan 3, 2007 #4

    cristo

    User Avatar
    Staff Emeritus
    Science Advisor

    In order to put 4 over the denominator 2, you must first multiply it by 2. Let's consider a general example: [tex] \frac{a}{b}+\frac{c}{d}=\frac{ad+cb}{bd} [/tex]

    Now applying this to your case we have, strictly speaking, [tex]\frac{4}{1}+\frac{n-1}{2}=\frac{2(4)+1(n-1)}{2}=\frac{8+n-1}{2} [/tex]
     
    Last edited: Jan 3, 2007
  6. Jan 3, 2007 #5
    Thanks for your help.

    I understand it now.

    Cathy
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Help with a C1 level question
  1. Help with level curves (Replies: 8)

Loading...