A community for students.

Here's the question you clicked on:

55 members online
  • 0 replying
  • 0 viewing

Loser66

  • one year ago

I don't understand. Please, help How many diagonals are there in a polygon with 9 sides? The answer is 36

  • This Question is Closed
  1. Loser66
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 0

    With 9 nodes, we pick 2 nodes to form a diagonal, hence there is 9C2 ways to get the diagonals that is 36 ways

  2. jim_thompson5910
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 1

    https://www.mathsisfun.com/geometry/polygons-diagonals.html

  3. Loser66
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 0

    However, with the formula \(\dfrac{n(n-3)}{2}\) we get \(dfrac{9(9-3)}{2}=27\) :(

  4. jim_thompson5910
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 1

    There are n vertices. You can choose n-3 other vertices to make a segment. You cannot choose the two neighboring vertices or the original vertex itself. That's why the "n-3" is there

  5. jim_thompson5910
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 1

    the /2 portion is to correct for double counting

  6. Loser66
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 0

    But the 2 answers didn't match. The first one is 36, the second one is 27 , how?

  7. jim_thompson5910
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 1

    36 is incorrect. It must be a typo

  8. jim_thompson5910
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 1

    If it asked "how many distinct line segments can be formed with 9 points?", then the answer would be 36

  9. Loser66
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 0

    question 3 http://www.testpreppractice.net/practice-tests/problem-solving-sm/pssm1.html?testname=GRE

  10. jim_thompson5910
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 1

    maybe instead of diagonals, they just meant how many segments were possible

  11. Loser66
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 0

    They confuse me a lot. I interpreted it as above, we pick 2 vertices to form a diagonal, hence 9C2 is what they did. But the formula on your site tells me other thing. That's why I make question here. One more thing, 9C2 is a valid logic, right?

  12. jim_thompson5910
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 1

    or maybe they redefined "diagonal", but that doesn't make much sense really

  13. Loser66
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 0

    Ok, let me try on smaller number of sides of a polygon. Thanks for clarifying it.

  14. Loser66
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 0

    Yes, I think your site is better, just look at a rectangular. Obviously it has 2 diagonals, but if 4C2 = 6 which is total segments on a rectangular, hhehehe.!!!

  15. Not the answer you are looking for?
    Search for more explanations.

    • Attachments:

Ask your own question

Sign Up
Find more explanations on OpenStudy
Privacy Policy

Your question is ready. Sign up for free to start getting answers.

spraguer (Moderator)
5 → View Detailed Profile

is replying to Can someone tell me what button the professor is hitting...

23

  • Teamwork 19 Teammate
  • Problem Solving 19 Hero
  • You have blocked this person.
  • ✔ You're a fan Checking fan status...

Thanks for being so helpful in mathematics. If you are getting quality help, make sure you spread the word about OpenStudy.

This is the testimonial you wrote.
You haven't written a testimonial for Owlfred.