Here's the question you clicked on:

55 members online
  • 0 replying
  • 0 viewing

Confucious

  • 4 years ago

I'm not good with logs, can someone help me? log(x+2)+log(x-1)=1

  • This Question is Closed
  1. henkjan
    • 4 years ago
    Best Response
    You've already chosen the best response.
    Medals 1

    log(x+2)+log(x-1) = log ((x+2)(x-1)) maybe that helps ;P

  2. henkjan
    • 4 years ago
    Best Response
    You've already chosen the best response.
    Medals 1

    And perhaps another helpful rule: if log(a)=b than 10^b = a only in the case when 10 is the basenumber of the logaritm, but if it is not stated otherwise it is always 10.

  3. henkjan
    • 4 years ago
    Best Response
    You've already chosen the best response.
    Medals 1

    So (x+2)(x-1) = 10^1 x^2+x-2= 10 x^2+x-12 = 0 Solve for x and find x = -4 and x = 3

  4. Confucious
    • 4 years ago
    Best Response
    You've already chosen the best response.
    Medals 0

    but it's equal to one??, in the first line you have the equation equal to 10

  5. henkjan
    • 4 years ago
    Best Response
    You've already chosen the best response.
    Medals 1

    I applied the rule I explained in my second post here. because b is in this case 1, it means that 10^1 = a a = (x-1)(x+2) in this case

  6. Confucious
    • 4 years ago
    Best Response
    You've already chosen the best response.
    Medals 0

    isn't the b 10?

  7. henkjan
    • 4 years ago
    Best Response
    You've already chosen the best response.
    Medals 1

    no, the b is equal to the right side in this equation log ((x+2)(x-1)) =1 ...... so it's 1

  8. Confucious
    • 4 years ago
    Best Response
    You've already chosen the best response.
    Medals 0

    okay

  9. Confucious
    • 4 years ago
    Best Response
    You've already chosen the best response.
    Medals 0

    so if the equation was equal to 2 the b would be 10^2?

  10. henkjan
    • 4 years ago
    Best Response
    You've already chosen the best response.
    Medals 1

    log(x)+log(y) = log(x*y) if log(a)=b then 10^b = a only 2 rules I used

  11. henkjan
    • 4 years ago
    Best Response
    You've already chosen the best response.
    Medals 1

    yes, indeed than it would be a = 10^2 = 100

  12. Confucious
    • 4 years ago
    Best Response
    You've already chosen the best response.
    Medals 0

    :) alright, the answer at the back of the text is just 3, why isn't the -4 acceptable?

  13. henkjan
    • 4 years ago
    Best Response
    You've already chosen the best response.
    Medals 1

    oh, right.... a logaritmic can never have a negative number log(-x) is not possible... as 10^b = a ... a can only become positive in this formula

  14. Confucious
    • 4 years ago
    Best Response
    You've already chosen the best response.
    Medals 0

    oh okay, thank you very much

  15. Not the answer you are looking for?
    Search for more explanations.

    • Attachments:

Ask your own question

Sign Up
Find more explanations on OpenStudy
Privacy Policy