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Evalute limit

  1. Jun 4, 2004 #1
    I’m reviewing an assignment that didn’t go so well

    Evaluate limit

    lim x->-1 (1/2+(x/(x+3))/(x+1)

    I reduced to (1+2x)/2 = -1/2

    I originally had x-1/x=2 but i redid the problem as above

    Is this correct?
  2. jcsd
  3. Jun 4, 2004 #2
    No, the answer is 3/4.


    You want to multiply both the numerator and denominator by x+3 so that you can get rid of the fraction in the numerator. Then it should be easy to factor x+1 out of both the numerator and denominator.
    Last edited: Jun 4, 2004
  4. Jun 4, 2004 #3
    That's not the correct answer. You want to find:

    \lim_{x\rightarrow -1} \frac{\frac{1}{2} + \frac{x}{x+3}}{x+1}

    Move the (x+1) up into the numerator:

    \frac{1}{2(x+1)} + \frac{x}{(x+3)(x+1)}

    Get a common denominator and add these two terms together, and you should see that the x+1 will fall out of the top and bottom.

    Edit: master_coda's way of multiplying the top and bottom by (x+3) is probably simpler.

    You should get 3/4, like master_coda said.

    Like I said in another of your threads, you can check your work by plugging in a value close to -1 into your original expression (like -0.99999). Your numerical result should be close to the analytical answer. If they aren't, you've probably made a mistake.
    Last edited: Jun 4, 2004
  5. Jun 4, 2004 #4

    I'm a newbie ...

    Are you using software to write the equation in that format?
  6. Jun 4, 2004 #5
    It's LaTeX markup (code), built into these forums. Check out this thread:


    The best way to learn is by example. You can click on any equation in any thread and see what the author typed to create it.
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