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anonymous

  • 5 years ago

how do i solve y=x^2-4x-45 to find all x intercepts

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  1. anonymous
    • 5 years ago
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    Factor!

  2. anonymous
    • 5 years ago
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    How do you do that? can you help?

  3. anonymous
    • 5 years ago
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    Well you want to make it into (x+a)(x+b) form

  4. anonymous
    • 5 years ago
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    so when you remultiply it it gives you x^2+ax+bx+ab

  5. anonymous
    • 5 years ago
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    what are some values of a and b that could give you ab=-45?

  6. anonymous
    • 5 years ago
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    9 and 5

  7. anonymous
    • 5 years ago
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    right, note that one of them needs to be negative. Now how would you make ax+bx = -4x from your 9 and 5?

  8. anonymous
    • 5 years ago
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    -5

  9. anonymous
    • 5 years ago
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    is the answer possibly 5 and -9?

  10. anonymous
    • 5 years ago
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    why yes it is. so what does your y=(x+a)(x+b) become?

  11. anonymous
    • 5 years ago
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    (x-5) and (x+9)

  12. anonymous
    • 5 years ago
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    you have your a and b values backwards actually. when you multiply (x-5)(x+9) = x^2+4x-45

  13. anonymous
    • 5 years ago
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    so its -9 and +5?

  14. anonymous
    • 5 years ago
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    yes those are your a and b values. Next you need to find values of x to provide 0=(x-9)(x+5) those will be when your y=0

  15. anonymous
    • 5 years ago
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    NO WAIT -5 and 9

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