Here's the question you clicked on:

55 members online
  • 0 replying
  • 0 viewing

alexd00d

  • 3 years ago

a+b+c=4 a^2+b^2+c^2=10 a^3+b^3+c^3=22 find the values of a, b ,and c

  • This Question is Closed
  1. alexd00d
    • 3 years ago
    Best Response
    You've already chosen the best response.
    Medals 0

    cubic polynominals

  2. liza2
    • 3 years ago
    Best Response
    You've already chosen the best response.
    Medals 0

    I have no idea, I'm commenting so that I'll get a notification when someone solves this.

  3. alexd00d
    • 3 years ago
    Best Response
    You've already chosen the best response.
    Medals 0

    If someone gets this they are the smartest person I know!

  4. joemath314159
    • 3 years ago
    Best Response
    You've already chosen the best response.
    Medals 1

    First note that:\[(a+b+c)^2=a^2+b^2+c^2+2(ab+ac+bc)\Longrightarrow \]\[4^2=10+2(ab+ac+bc)\Longrightarrow ab+ac+bc=3\]Also:\[(a+b+c)^3=a^3+b^3+c^3+3(a+b+c)(ab+ac+bc)-3abc\Longrightarrow\]\[4^3=22+3(4)(3)-3abc\Longrightarrow abc=-2\]So your system is equivalent to: a+b+c=10 ab+ac+bc=3 abc=-2 Solving this system is the same as solving the polynomial: \[x^3-10x^2+3x+2=0\]So the solutions to this polynomial are the solutions to your system.

  5. joemath314159
    • 3 years ago
    Best Response
    You've already chosen the best response.
    Medals 1

    oh, mistype, thats why things were acting weird. Your system is equivalent to:\[a+b+c=4\]\[ab+ac+bc=3\]\[abc=-2\]which gives the polynomial:\[x^3-4x+3x-2=0\]which gives solutions \[a= 2, b=1-\sqrt{2}, c=1+\sqrt{2}\]

  6. joemath314159
    • 3 years ago
    Best Response
    You've already chosen the best response.
    Medals 1

    mistype again, +2 instead of -2 >.>

  7. alexd00d
    • 3 years ago
    Best Response
    You've already chosen the best response.
    Medals 0

    You must have had loads of practice to be as good as you are!

  8. 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