Results 1 to 4 of 4

Math Help - Can someone check if i done the questions correctly: Limits

  1. #1
    Junior Member
    Joined
    Sep 2008
    Posts
    34

    Can someone check if i done the questions correctly: Limits

    Q1:
    Can someone check if i done the questions correctly: Limits-1.jpg
    lim 2x^3 squareroot(x+6)
    x->3

    I substitute in the 3
    =2(3)^3 squareroot(3+6)
    =(54)(3)
    =162
    I'm not sure if 162 is the limit or not.. the number seems huge

    =================

    Q2:
    Can someone check if i done the questions correctly: Limits-2.jpg
    lim (64-x^2)/(squareroot(8-x))
    x-> negative infinity

    First i found the greatest degree in the denominator
    = squareroot of x

    =((64/squareroot x)-(x^2/ squareroot x))/(squareroot (x(8/x-1))
    =substitute in negative infinity
    =-1/squareroot x
    =0

    Thanks
    Last edited by hovermet; September 20th 2011 at 10:52 PM.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Joined
    Aug 2007
    From
    USA
    Posts
    3,110
    Thanks
    2

    Re: Can someone check if i done the questions correctly: Limits

    Q2 "substitute in negative infinity" -- Seriously? Please never do that. "negative infinity" is NOT a number. Plus, you don't know it the function is continuous. Why are you substituting at all?

    Let's assume that as x increases without bound in the negative direction that it eventually decreases below -8. (Why did I bother to say that?)

    For x < -8, \frac{64-x^{2}}{\sqrt{8-x}}\;=\;-\sqrt{\frac{\left(64-x^{2}\right)^{2}}{8-x}}

    Does that do anything for our hunt for the limit?
    Last edited by TKHunny; September 21st 2011 at 03:43 AM.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member
    Joined
    Sep 2008
    Posts
    34

    Re: Can someone check if i done the questions correctly: Limits

    I stared this for quite a while, I don't know how to continue on. You said so because the domain is x<8? Whats within sqrt must be >=0 and the denominator must not equal 0
    can the this function be further simplified?
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor Siron's Avatar
    Joined
    Jul 2011
    From
    Norway
    Posts
    1,250
    Thanks
    20

    Re: Can someone check if i done the questions correctly: Limits

    Notice that: (64-x^2)=(8-x)(8+x) therefore:
    -\sqrt{\frac{(64-x^2)^2}{8-x}}=-\sqrt{\frac{(8-x)^2(8+x)^2}{8-x}}=-\sqrt{(8+x)^2(8-x)}
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 12
    Last Post: May 26th 2011, 08:48 AM
  2. Replies: 3
    Last Post: February 14th 2009, 01:43 AM
  3. Replies: 2
    Last Post: February 14th 2009, 01:38 AM
  4. Can you check if I integrated correctly?
    Posted in the Calculus Forum
    Replies: 3
    Last Post: November 30th 2008, 10:28 AM
  5. please check if I answered correctly
    Posted in the Algebra Forum
    Replies: 1
    Last Post: October 21st 2008, 09:48 AM

Search Tags


/mathhelpforum @mathhelpforum