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anonymous

  • 4 years ago

Solve 2log(x+1)-log(5x+1)+log(x-1)=log2.

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  1. anonymous
    • 4 years ago
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    star with \[\log(\frac{(x+1)^2(x-1)}{5x+1})=\log(2)\]

  2. anonymous
    • 4 years ago
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    okay yeah i did that, i'm not sure how to move from there :S the answer is supposed to be 3.

  3. anonymous
    • 4 years ago
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    oh carp you are going to end up with a cubic polynomial. oh well...

  4. anonymous
    • 4 years ago
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    \[(x+1)^2(x-1)=2(5x+1)\]

  5. anonymous
    • 4 years ago
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    \[x^3+x^2-11 x-3 = 0\]

  6. anonymous
    • 4 years ago
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    how you are supposed to solve this is anyone's guess, but if there is a rational solution it has to be either 3 or -3 so i imagine you are supposed to try 3 and see that it works

  7. anonymous
    • 4 years ago
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    then you have to factor as \[(x-3)(x^2+4x+1)\] and see that the other two zeros are negative

  8. anonymous
    • 4 years ago
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    oh so i would use quadratic formula to solve the second set?

  9. anonymous
    • 4 years ago
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    yes, but both answers are negative so you can disregard them because you would end up taking a log of a negative number, which is not defined

  10. anonymous
    • 4 years ago
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    what do you mean by "you would end up taking a log of a negative number, which is not defined", didn't we drop the logs though?

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spraguer (Moderator)
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