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jenejij Group Title

If the graph of the quadratic function f(x) = x^2 + dx +3d has its vertex on the x axis what are the possible values of d? What if f(x) = x^2 + 3dx +1?

  • 2 years ago
  • 2 years ago

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  1. mukushla Group Title
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    complete the square for x^2 + dx +3d to get its vertex

    • 2 years ago
  2. meera_yadav Group Title
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    mukushla is right :) try doing ...

    • 2 years ago
  3. jenejij Group Title
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    I have the answers. Easily accessible in the back of the book. How to solve it is the problem. When you say complete the square what do you mean? I've been trying x^2 + dx +3d = ax^2 + (-2ah)x+ (ah^2+k) And trying to identify the vertex.. that waayy... But what do you mean by complete the square?

    • 2 years ago
  4. k.rajabhishek Group Title
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    the vertex of quadratic equation is given by (-b/2a, c-b^2/4a) since it has vertex on X axis therefore y ordinate =0 . hence c-b^2=0

    • 2 years ago
  5. jenejij Group Title
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    Thanks! I'll try it again.

    • 2 years ago
  6. k.rajabhishek Group Title
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    in 1st case the value of d=0 and 3 in 2nd case d=1/3 and -1/3

    • 2 years ago
  7. mukushla Group Title
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    @jenejij take a look http://www.mathsisfun.com/algebra/completing-square.html

    • 2 years ago
  8. jenejij Group Title
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    Oh okay. I know how to "complete the square" haha. Got it. =)

    • 2 years ago
  9. jenejij Group Title
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    Thanks everyone =)

    • 2 years ago
  10. jenejij Group Title
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    Actually - still having problems.. =/ I don't think x=3. x= 0, and x= 12.

    • 2 years ago
  11. k.rajabhishek Group Title
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    x=12 is not right answer

    • 2 years ago
  12. jenejij Group Title
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    thats what the answer in the back of my text book is... but I don't know how to get there.

    • 2 years ago
  13. k.rajabhishek Group Title
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    what is the final answer of first part?

    • 2 years ago
  14. jenejij Group Title
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    d = 0 and d= 12. According the the textbook...

    • 2 years ago
  15. k.rajabhishek Group Title
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    and for second part ??

    • 2 years ago
  16. jenejij Group Title
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    \[d = + or - 2 / \sqrt{13}\]

    • 2 years ago
  17. k.rajabhishek Group Title
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    wait

    • 2 years ago
  18. k.rajabhishek Group Title
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    I got the answer: plz check it

    • 2 years ago
  19. k.rajabhishek Group Title
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    the value of x coordinate of vertex is given by -b/2a; from the given question we have a=1 b=d c=3d substituting the values in -b/2a we have -d/2

    • 2 years ago
  20. k.rajabhishek Group Title
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    to find y ordinate substitute this value in the given eq. we have |dw:1341572810912:dw|

    • 2 years ago
  21. jenejij Group Title
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    |dw:1341572956794:dw|

    • 2 years ago
  22. jenejij Group Title
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    I circled that thing.. is it d?

    • 2 years ago
  23. k.rajabhishek Group Title
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    since it has vertex on x axis thus y=0 hence we have d^2/4 - d^2/2 +3d = 0 on solving we have d=0 and 12

    • 2 years ago
  24. k.rajabhishek Group Title
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    yes it is d

    • 2 years ago
  25. k.rajabhishek Group Title
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    have u understood ??

    • 2 years ago
  26. jenejij Group Title
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    yes Thank you!!!

    • 2 years ago
  27. k.rajabhishek Group Title
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    similarly u can do second part .. plz do it and tell me have u got the answer or not

    • 2 years ago
  28. jenejij Group Title
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    okay I will work on it

    • 2 years ago
  29. k.rajabhishek Group Title
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    give me a medal .........lol

    • 2 years ago
  30. jenejij Group Title
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    \[x^2 + 3dx - d^2 +1 then 0 = (-d/2)^2 +3d(-d/2) - d^2 + 1 \]

    • 2 years ago
  31. jenejij Group Title
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    \[(d/4)^2 + -3d^2/2 -d^2 +1 = 0 \]

    • 2 years ago
  32. k.rajabhishek Group Title
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    no; for second part u again need to find the x coordinate and follow the same steps

    • 2 years ago
  33. k.rajabhishek Group Title
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    since it was a different equation

    • 2 years ago
  34. jenejij Group Title
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    okay let me try again. toss that grain of salt my way (I've been working all night.. it's 4:21 am) I'm not usually this bad haha

    • 2 years ago
  35. k.rajabhishek Group Title
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    no problem: from which country u r from ??

    • 2 years ago
  36. jenejij Group Title
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    US.

    • 2 years ago
  37. jenejij Group Title
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    okay so then is 3d = -b/2a?

    • 2 years ago
  38. jenejij Group Title
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    no. wait.

    • 2 years ago
  39. jenejij Group Title
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    I can't think. I have to do this in the morning. Thanks so far.

    • 2 years ago
  40. k.rajabhishek Group Title
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    give me 1 min, let me tell you

    • 2 years ago
  41. k.rajabhishek Group Title
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    in second part : a=1 b=3d c=1 now subs. in -b/2a u have -3d/2

    • 2 years ago
  42. jenejij Group Title
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    okay. I was on the right track. but not quite there.

    • 2 years ago
  43. jenejij Group Title
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    hmm

    • 2 years ago
  44. k.rajabhishek Group Title
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    then put this value of x in original equation x^2+3dx+1=0|dw:1341574077931:dw|

    • 2 years ago
  45. jenejij Group Title
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    Okay. I see the answer. And I understand, but without sleep I won't reeeally get it. Again thank you for your help.

    • 2 years ago
  46. k.rajabhishek Group Title
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    bye i had sent u mail plz check it

    • 2 years ago
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