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anonymous

  • one year ago

f(x)=-1/2x^2+7x-2. x=7. Im trying to find the vertex, one is 7, and the other is 45/2. I keep getting 49/2. what am I missing?

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  1. anonymous
    • one year ago
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    what does "one is 7" mean?

  2. anonymous
    • one year ago
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    first coordinate of the vertex is always \(-\frac{b}{2a}\) in your case \(a=-\frac{1}{2},b=7\)

  3. anonymous
    • one year ago
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    ooh i see "one is 7" means the first coordinate is 7

  4. anonymous
    • one year ago
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    \[f(7)=-\frac{1}{2}\times 7^2+7\times 7-2\]

  5. anonymous
    • one year ago
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    that was supposed to be x=7 not one is 7

  6. anonymous
    • one year ago
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    i see exactly what you are missing you did not subtract 2 at the end

  7. anonymous
    • one year ago
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    if I subtract 2 from \[\frac{ 49 }{ 2}\] how does that equal \[\frac{ 45 }{ 2 }\]?

  8. anonymous
    • one year ago
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    ?

  9. anonymous
    • one year ago
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    the vertex is (7, 45/2). I cant figure out how its not 49/2. the class im in offers no explanation as to how it gets the answers, so im floored on how 7x7 equals 45.

  10. anonymous
    • one year ago
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    ok lets go slow

  11. anonymous
    • one year ago
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    did you get that you find the second coordinate of the vertex by finding \[f(7)=-\frac{1}{2}\times 7^2+7\times 7-2\]

  12. anonymous
    • one year ago
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    yes, I got that far find and this is what I did, in order (7)^2=49. 7x7=49-2=47 so then I have \[-\frac{ 1 }{ 2 }(49)+47\]

  13. anonymous
    • one year ago
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    you lost me entirely

  14. anonymous
    • one year ago
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    \[-\frac{1}{2}\times 7^2+7\times 7-2\\ -\frac{1}{2}\times 49+47-2\\ -\frac{49}{2}+\frac{98}{2}-2\\ \frac{49}{2}-2\\ \frac{45}{2}\]

  15. anonymous
    • one year ago
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    typo there , the second line should have 2 49's in it

  16. campbell_st
    • one year ago
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    just remember \[-2 =- \frac{4}{2}\]

  17. campbell_st
    • one year ago
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    so you have \[\frac{49}{2} - \frac{4}{2} = \frac{45}{2}\]

  18. anonymous
    • one year ago
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    okay thank you I didn't know how to get the second fraction. I see it know. I wish my class program would just explain it seesh. thanks again!

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