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vivalakoda

Solve for x?

  • one year ago
  • one year ago

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  1. vivalakoda
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    \[-4\sqrt{x+9}=20 \]

    • one year ago
  2. AntarAzri
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    sqrt(x+9)=-(20/4)

    • one year ago
  3. vivalakoda
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    I know how to solve is, I'm just not sure how to get rid of the -4 in the front of the radical.

    • one year ago
  4. Ladyalice25
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    you need to remove the square from x+9 the way you do that is by squaring both side and you end up with x+9=-(20/4)^2. then solve from there.

    • one year ago
  5. AntarAzri
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    yes that 's it

    • one year ago
  6. Ladyalice25
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    x+9=-20/4)^2. -20/4^2 = -25 then take -25 subtract 9. you will get the answer of x=-34

    • one year ago
  7. dpaInc
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    it's easy to see that this has NO SOLUTION: (-4)*(-5) = 20 so that means: \(\large -4\sqrt{x+9}=20 \rightarrow \sqrt{x+9}=-5\) \(\large \sqrt{x+9}=-5\) which has no solution because the left side is always positive but the right side is negative

    • one year ago
  8. vivalakoda
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    Can't you just square both sides to get rid of the square root, then solve like an equation?

    • one year ago
  9. dpaInc
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    yes you can try to do that... it's one technique you should try to solve it. but why continue when you know this is an impossible equation to solve?

    • one year ago
  10. dpaInc
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    not impossible, no solution... if you do solve it, the solution is an extraneous solution....

    • one year ago
  11. vivalakoda
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    If according to your answer it is √x+9 = -5 then you'd square both sides to have: x+9 = -25 subtract 9 from both sides and get -16 as x?

    • one year ago
  12. AntarAzri
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    Difficult equation in history

    • one year ago
  13. dpaInc
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    squaring both sides you get positive 25

    • one year ago
  14. vivalakoda
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    Oh, that's right thanks so then x+9=25 subtract 9 then positive 16?

    • one year ago
  15. dpaInc
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    yes... now let's see if the solution of x=16 works....

    • one year ago
  16. AntarAzri
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    no no no no =-20

    • one year ago
  17. AntarAzri
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    that's wrong

    • one year ago
  18. dpaInc
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    \(\large (-4)(\sqrt{x+9})=20 \) \(\large (-4)(\sqrt{\color {red}{16}+9})=20 \) \(\large (-4)(\sqrt{\color {red}{25}})=20 \) \(\large -4 \cdot 5 = 20 \) \(\large -20=20 \) ???? not a true statement

    • one year ago
  19. dpaInc
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    so the solution of x=16 is extraneous and not really a solution.

    • one year ago
  20. AntarAzri
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    solution \[\left| -4 \right|\]

    • one year ago
  21. AntarAzri
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    suggestion hhhh

    • one year ago
  22. dpaInc
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    @AntarAzri , what's the solution?

    • one year ago
  23. AntarAzri
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    \[\left| -4 \right|\]

    • one year ago
  24. dpaInc
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    \(\large (-4)(\sqrt{x+9})=20 \) \(\large (-4)(\sqrt{|-4|+9})=20 \) \(\large (-4)(\sqrt{4+9})=20 \) \(\large (-4)(\sqrt{13})=20 \) x=|-4| doesn't seem to work. That's not a solution.

    • one year ago
  25. vivalakoda
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    my oh my I have headaches because of this problem..

    • one year ago
  26. AntarAzri
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    no no i dont mean the x |−4|=4

    • one year ago
  27. dpaInc
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    ok. whatever... my answer stands... NO SOLUTION to the equation: \(\large (-4)(\sqrt{x+9})=20 \) \)

    • one year ago
  28. AntarAzri
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    \[(\left| -4 \right|)(\sqrt{16+9})=20\]

    • one year ago
  29. dpaInc
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    here's wolframs answer: http://www.wolframalpha.com/input/?i=solve+-4*sqrt%28x%2B9%29%3D20

    • one year ago
  30. AntarAzri
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    good

    • one year ago
  31. AntarAzri
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    http://www.wolframalpha.com/input/?i=solve+|%E2%88%924|*sqrt%28x%2B9%29%3D20

    • one year ago
  32. vivalakoda
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    ?

    • one year ago
  33. dpaInc
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    if u don't understand my answer and expanation maybe someone else can give u a better answer... i will not argue my point further....

    • one year ago
  34. AntarAzri
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    Do we agree that it can not be the root of a negative number gives a positive number ?

    • one year ago
  35. vivalakoda
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    I'll see what my teacher says when she grades it. Thanks for your time

    • one year ago
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