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justinee

  • 2 years ago

Can someone check this for me? (completing the square)

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  1. justinee
    • 2 years ago
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    y = -2x^2 - 20x - 48

  2. justinee
    • 2 years ago
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    then i rewrote that into: y = -2(x^2 - 20x ____) -48 -20/2 = -10 then square it and I got 100 y = -2(x^2 - 20x +100) -48

  3. justinee
    • 2 years ago
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    then I added 100 to both sides and I got: y + 100= -2(x - 10)^2 -48 -100 -100 ------------------------ y = -2(x - 10)^2 - 148

  4. halorazer
    • 2 years ago
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    You subtracted 100 though ^

  5. Decart
    • 2 years ago
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    you add 48 to the other side and then also the 100 and the quadratic = 148

  6. Decart
    • 2 years ago
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    then you can factor the left side

  7. justinee
    • 2 years ago
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    can you show me that in steps? like from the beginning

  8. Decart
    • 2 years ago
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    you did it rite just set the equation = 0 then subtract 49 from both sides so 2x^2-20x=48

  9. Decart
    • 2 years ago
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    then complete the square and add the 100 to both sides

  10. justinee
    • 2 years ago
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    so it'd be 0 = -2(x^2 - 20x + 100) -48 ?

  11. justinee
    • 2 years ago
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    why do I need to factor that

  12. justinee
    • 2 years ago
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    Ok I got it thanks! and one more question

  13. justinee
    • 2 years ago
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    How would I solve: x^2 - 38x + c also by completing the square

  14. Decart
    • 2 years ago
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    c is a constant most likely just move it to the other side and complete the square

  15. justinee
    • 2 years ago
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    what is that going to give me?

  16. Decart
    • 2 years ago
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    x^2-38x=c

  17. justinee
    • 2 years ago
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    and what would be the next step

  18. justinee
    • 2 years ago
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    0 = (x2 - 38x ___) +c ?

  19. Decart
    • 2 years ago
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    square the -38 and do the same to both sides

  20. Decart
    • 2 years ago
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    (x^2-38x+__)=__-c

  21. justinee
    • 2 years ago
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    -38/2 = -19^2 = 361

  22. Decart
    • 2 years ago
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    yup

  23. Decart
    • 2 years ago
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    so that is on both sides

  24. Decart
    • 2 years ago
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    (x^2-38x+361)=361-c

  25. justinee
    • 2 years ago
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    okay so far i have: (x^2 - 38x + 361) = 361 -c

  26. Decart
    • 2 years ago
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    right now you should be able to factor the quadratic which is the point of completing the square

  27. justinee
    • 2 years ago
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    so like: ____ x___ = 361 ____+___= -38

  28. Decart
    • 2 years ago
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    right it will be the same number it is squared

  29. justinee
    • 2 years ago
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    -19

  30. Decart
    • 2 years ago
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    yup

  31. justinee
    • 2 years ago
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    (x-19)^2 = 361 - c?

  32. Decart
    • 2 years ago
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    and the first equation was x^2-10+25=49

  33. Decart
    • 2 years ago
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    right

  34. justinee
    • 2 years ago
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    what do I do now?

  35. Decart
    • 2 years ago
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    with the second you can't do anything it is most likely to show how you did the work

  36. Decart
    • 2 years ago
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    x-5=7

  37. justinee
    • 2 years ago
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    so just that ^

  38. justinee
    • 2 years ago
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    how would i write tht in intercept form

  39. Decart
    • 2 years ago
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    do you mean y=mx+b

  40. justinee
    • 2 years ago
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    no I also have to rewrite tht in intercept

  41. Decart
    • 2 years ago
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    the x intercept is +or-(7/5,0)

  42. Decart
    • 2 years ago
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    that is the y is 0

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