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wolf

  • 5 years ago

y=x^2-2x-15 how do you find the vertex?

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  1. Wolf
    • 5 years ago
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    and the x intercepts are at 5 and -3?

  2. anonymous
    • 5 years ago
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    begin by completing the square

  3. anonymous
    • 5 years ago
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    to find the 'x' coordinate of the vertex, use x = -b/2a or similarly take the first derivative, set equal to zero and solve for 'x'. To find the 'y' coord. just plug the 'x' value into the original equation.

  4. anonymous
    • 5 years ago
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    Yes, the 'x' intercepts are 5 and -3: (x+3)(x-5) = 0

  5. Wolf
    • 5 years ago
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    and vertex at 1,-16

  6. anonymous
    • 5 years ago
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    if you complete the square you'll arrive at \[y=(x-1)^{2}+13\] This is the standard form for a parabola. From this form, we then know that the vertex is at (1, 13)

  7. Wolf
    • 5 years ago
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    oops i messed up haha

  8. anonymous
    • 5 years ago
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    oops, me too. Sorry

  9. Wolf
    • 5 years ago
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    -1,-12?

  10. anonymous
    • 5 years ago
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    y=(x−1)2+14 so the vertex is at (1, 14)

  11. Wolf
    • 5 years ago
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    obviously the derivative thing isnt working for me ahha

  12. anonymous
    • 5 years ago
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    that should work too. Take the first derivative: dy/dx=2x-2 set the first derivative equal to zero: 2x-2=0, x = 1

  13. anonymous
    • 5 years ago
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    plug in x= 1 to the original equation to find the y-coordinate of the vertex

  14. anonymous
    • 5 years ago
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    I got the coordinates of the vertex to be (1,-16)... After plugging in x=1. I may be wrong.

  15. Wolf
    • 5 years ago
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    but when i plug 1 in i get -16?

  16. Wolf
    • 5 years ago
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    which is what i had the first time before i got confused

  17. anonymous
    • 5 years ago
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    y(1)=\[y(1) = 1^{2}-2+15=14\]

  18. Wolf
    • 5 years ago
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    -15

  19. Wolf
    • 5 years ago
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    thats what you were doing wrong jjanelle haha

  20. anonymous
    • 5 years ago
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    1-2+15=14

  21. anonymous
    • 5 years ago
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    Oh, janelle, you got the -15 mixed up

  22. Wolf
    • 5 years ago
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    hahah thank yall

  23. anonymous
    • 5 years ago
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    I can't read, good call.

  24. anonymous
    • 5 years ago
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    :)

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