Results 1 to 9 of 9

Math Help - delta!!

  1. #1
    Member
    Joined
    Oct 2006
    Posts
    78

    delta!!

    hi to all members i am new here hehe tuesday my school started and i have homework to do for tommorow plz help

    soit s un nombre reel donne.parmi tous lescouples(alfa,beta) de nb reels dont la somme est s,quel est celui dont le produit p=alfa.beta maximum ??
    it's french but plz help!!!
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor Quick's Avatar
    Joined
    May 2006
    From
    New England
    Posts
    1,024

    Unhappy I'm just starting french 2

    Quote Originally Posted by iceman1 View Post
    soit s a real number give??.parmi all the couples(alpha,beta) of real numbers dont sum?? is s,which is celui dont the maximum product when p=alfa.beta??
    You're going to have to clarify...
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Grand Panjandrum
    Joined
    Nov 2005
    From
    someplace
    Posts
    14,972
    Thanks
    4
    Quote Originally Posted by iceman1 View Post
    hi to all members i am new here hehe tuesday my school started and i have homework to do for tommorow plz help

    soit s un nombre reel donne.parmi tous lescouples(alfa,beta) de nb reels dont la somme est s,quel est celui dont le produit p=alfa.beta maximum ??
    it's french but plz help!!!
    Why did you not translate it for us?

    My translation is:

    Let S be the set of all pairs of reals (alpha, beta), such that alpha+beta=s.
    What is the maximum of p=alpha.beta?

    RonL
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor Quick's Avatar
    Joined
    May 2006
    From
    New England
    Posts
    1,024
    Quote Originally Posted by iceman1 View Post
    soit s un nombre reel donne.parmi tous lescouples(alfa,beta) de nb reels dont la somme est s,quel est celui dont le produit p=alfa.beta maximum ??
    Quote Originally Posted by Free Online Translator
    or s a reel number gives among all couples (alfa, beta) of nb reels whose sum is s, which is the one maximum of which produces it p=alfa.beta
    you should always translate before asking the question (even if it's as botchy as the internet translators)...
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Grand Panjandrum
    Joined
    Nov 2005
    From
    someplace
    Posts
    14,972
    Thanks
    4
    Quote Originally Posted by CaptainBlack View Post
    Why did you not translate it for us?

    My translation is:

    Let S be the set of all pairs of reals (alpha, beta), such that alpha+beta=s.
    What is the maximum of p=alpha.beta?

    RonL
    beta=s-alpha,

    so

    p=alpha(s-alpha)=-alpha^2+s.alpha

    this has a maximum when ds/d(alpha)=0 (you will have to show this is a maximum rather
    than a minimum), or:

    -2.alpha + s=0,

    or

    alpha=s/2.

    RonL
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Member
    Joined
    Oct 2006
    Posts
    78
    lol tnx mate for the traslation and for this results tnx alot

    my second probleme??

    we have 4 carres de cote respective a,a+1,a+2,a+3...u can choose a pour l'air du plus grand=somme des autres??

    and tnx
    Follow Math Help Forum on Facebook and Google+

  7. #7
    Member
    Joined
    Oct 2006
    Posts
    78

    translation for english!!!

    lol tnx mate for the traslation and for this results tnx alot

    my second probleme??

    One has access to four carees of respective a,a+1,a+2,a+3. quotations can one to choose has for that the air of the biggest one be
    egale has the sum of the others

    plz help now


    P a number reel donne.parmi all the couples (esparto, beta) of number reels of which produced it is p,quel the one of which the sum s = esparto + beta is minimum?


    help me 2 hours and my class started
    Follow Math Help Forum on Facebook and Google+

  8. #8
    Grand Panjandrum
    Joined
    Nov 2005
    From
    someplace
    Posts
    14,972
    Thanks
    4
    Quote Originally Posted by iceman1 View Post
    lol tnx mate for the traslation and for this results tnx alot

    my second probleme??

    One has access to four carees of respective a,a+1,a+2,a+3. quotations can one to choose has for that the air of the biggest one be
    egale has the sum of the others
    Lets assume that this is telling us that we have four crates of similar form
    with charateristic dimensions a, a+1, a+2, a+3. The largest has a volume
    equal to the sum of the volumes of the other three, find a.

    The volumes are proportional to the cube of the charateristic dimension, so:

    (a+3)^3=a^3 + (a+1)^3 + (a+2)^3.

    This simplifies after expanding the cubes to:

    2a^3 - 12a -18 = 0.

    Which has a single real solution of a=3.

    RonL
    Follow Math Help Forum on Facebook and Google+

  9. #9
    Grand Panjandrum
    Joined
    Nov 2005
    From
    someplace
    Posts
    14,972
    Thanks
    4
    Quote Originally Posted by iceman1 View Post
    P a number reel donne.parmi all the couples (esparto, beta) of number reels of which produced it is p,quel the one of which the sum s = esparto + beta is minimum?
    Of all pairs of real numbers (alpha, beta) with product equal to p (best
    assume p>0 here), find that pair for which their sum s is a minimum.

    alpha.beta=p,

    so

    beta=p/alpha.

    Hence:

    s=alpha+beta=alpha+p/alpha.

    The minimum (if it exists) of s occurs when ds/d(alpha)=0

    ds/d(alpha)=1 - p/alpha^2

    So the alpha we are interested in is a root of:

    alpha^2 - p=0,

    or alpha=+/- sqrt(p)

    You probably want alpha and beta to be >=0, in which case the positive root is
    what you want, also you should justify that this is in fact a minimum.

    RonL
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Help. Can I do this? (Delta Epsilon)
    Posted in the Calculus Forum
    Replies: 2
    Last Post: March 21st 2010, 07:35 PM
  2. Replies: 0
    Last Post: October 27th 2009, 08:06 AM
  3. Replies: 2
    Last Post: September 29th 2009, 09:59 AM
  4. delta x
    Posted in the Math Topics Forum
    Replies: 3
    Last Post: December 9th 2008, 05:55 PM
  5. Delta?
    Posted in the Calculus Forum
    Replies: 16
    Last Post: August 22nd 2008, 07:15 PM

Search Tags


/mathhelpforum @mathhelpforum