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rach_ell Group Title

The function f(x)= kx^3 - 8x^2 -x + 3k + 1 has a zero when x=2. Determine the value of k. Graph f(x) and determine all the zeros. Then rewrite in factored form. I found that k=3 so far, but I'm not sure how to graph it without making a table of values, or how to find the zeros. Any ideas?

  • 10 months ago
  • 10 months ago

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  1. myininaya Group Title
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    So f is 0 when x=2 So write this f(2)=0 except actually evaluate the function given at x=2 Replace all of those x's with 2 and then set that result to 0.

    • 10 months ago
  2. rach_ell Group Title
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    I did that already to find the k value (3), but I'm stuck on the graphing part. And also on how to find the zeros.

    • 10 months ago
  3. myininaya Group Title
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    Do you know synthetic division?

    • 10 months ago
  4. rach_ell Group Title
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    We haven't learned that yet

    • 10 months ago
  5. myininaya Group Title
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    Do you know long division then?

    • 10 months ago
  6. rach_ell Group Title
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    yes

    • 10 months ago
  7. myininaya Group Title
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    Great. Since x=2 is a zero, then x-2 is a factor of 3x^3-8x^2-x+9+1

    • 10 months ago
  8. myininaya Group Title
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    See what another factor is by seeing how many times x-2 goes into 3x^3-8x^2-x+10

    • 10 months ago
  9. myininaya Group Title
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    I must leave but you should get a quotient and no remainder. You should be able to factor the quotient. You should be able to now find your 3 zeros. Test the intervals between and before and after each zero to see if the function is above or below the x-axis. Then connect the dots.

    • 10 months ago
  10. rach_ell Group Title
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    Thank you, I will try that!

    • 10 months ago
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