Quantcast

Got Homework?

Connect with other students for help. It's a free community.

  • across
    MIT Grad Student
    Online now
  • laura*
    Helped 1,000 students
    Online now
  • Hero
    College Math Guru
    Online now

Here's the question you clicked on:

55 members online
  • 0 replying
  • 0 viewing

Aryang

prove that x^8 -x^7 + x^2 -x +15 has no real root

  • one year ago
  • one year ago

  • This Question is Closed
  1. mukushla
    Best Response
    You've already chosen the best response.
    Medals 3

    for \(x\le0\) its obvious that \(x^8 -x^7 + x^2 -x +15 >0\) u just prove for \(x>0\) : \(x^8 -x^7 + x^2 -x +15 >0\)

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

    and does descartes' theorem help a great deal ? according to that,,it should have max 4 +ve roots..

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

    no need to descartes...

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

    well what then ?

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

    ohh wait,,leme try..

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

    well just show that \(x^8 -x^7 + x^2 -x +15>0\) for every real number

    • one year ago
  7. Yahoo!
    Best Response
    You've already chosen the best response.
    Medals 0

    descartes helps a lot lol

    • one year ago
  8. Yahoo!
    Best Response
    You've already chosen the best response.
    Medals 0

    http://mathworld.wolfram.com/DescartesSignRule.html

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

    for x>1 ,, x^8 > x^7 and x^2 >x so f(x) > 0 for x>1 for 0<x<1 , x> x^2 > x^7 > x^8 we then have 15 - (fraction + fraction) ,,which is obviously >0 so f(x) is always >0 am i right ?

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

    exactly

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

    ohh..thank you @mukushla your little hint only helped me a lot :)

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

    np...:)

    • one year ago
    • Attachments:

See more questions >>>

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.