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dang_thitham

  • 4 years ago

Find f(-2) if f(x) = 2x2 + kx + 2 and f(1) = 3.

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  1. dang_thitham
    • 4 years ago
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    need help

  2. anonymous
    • 4 years ago
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    replace x by 1 and solve \[f(1)=2+k+2=3\] for k

  3. dang_thitham
    • 4 years ago
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    k=-1?

  4. dang_thitham
    • 4 years ago
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    no it is wrong

  5. abtrehearn
    • 4 years ago
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    We find what k is by plugging 1nfor x into the original function and setting the result equal to 3: 2*1^2 + k*1 + 2 = 3, so k = -1, and the function is\[f(x) = 2x^{2} - x + 2.\]We evaluate this function at x = -2: f(-2) = 8.

  6. dang_thitham
    • 4 years ago
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    so what is its' result?

  7. abtrehearn
    • 4 years ago
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    I glitched. f(-2) = 12.

  8. dang_thitham
    • 4 years ago
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    why?

  9. abtrehearn
    • 4 years ago
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    Did you get k = -1?

  10. dang_thitham
    • 4 years ago
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    yes

  11. anonymous
    • 4 years ago
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    looks like if you solve larger less than twice the smaller. make x the larger then we get \[2+k+2=3\] you get \[k=-1\] yes? so now you have \[f(x)=2x^2-x+2\] and if you want \[f(-2)\] you compute \[f(-2)=2(-2)^2-(-2)+2\]

  12. dang_thitham
    • 4 years ago
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    oh ok

  13. abtrehearn
    • 4 years ago
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    You use the information to find the value of f(-2).

  14. dang_thitham
    • 4 years ago
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    ok I understand now.Thanks

  15. abtrehearn
    • 4 years ago
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    :^)

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