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  • CamaroKeith

    April 27, 2009 8:26 p.m. CamaroKeith New Reader

    I'm hoping someone can help here. I'm drawing a complete blank as to why you get this answer:

    1/2[1/(s-b)] + 1/2[1/(s+b)] = 1/2[(2s)/(s^2-b^2)] = s/(s^2-b^2)

    I'm good with the denominator but for the life of me I can't rationalize why you get "s" in the numerator.

    Any help is appreciated.

    -Keith

  • Hal

    April 27, 2009 8:37 p.m. Hal HalfDork

    Probably all wrong since the last math class I took was in 1963.

    1/2 of 2s = s

  • confuZion3

    April 27, 2009 8:37 p.m. confuZion3 Dork

    Alrighty then. I'll see if I can help you out with this.

  • NONACK

    April 27, 2009 8:43 p.m. NONACK New Reader

    Hal is right. What you get is 2s/2(s^2-b^2), then 2 cancels out, leaving you with s/(s^2-b^2)

    EDIT: See below post for intelligent, useful answer.

  • confuZion3

    April 27, 2009 8:50 p.m. confuZion3 Dork

    You multiply the whole thing by S/S (which = 1). That's how you get it in the numerator. Right?

    He wants to know how you come about with S in the numerator to begin with.

  • CamaroKeith

    April 27, 2009 9:05 p.m. CamaroKeith New Reader

    confuZion3 wrote:

    You multiply the whole thing by S/S (which = 1). That's how you get it in the numerator. Right?

    Actually you have to multiply the 2 denominators together:

    (s+b)(s-b) = s^2-sb + bs - b^2 = s^2 - b^2

    I can't remember what you do to the numerators tho and how you wind up with 2s

  • mith612

    April 27, 2009 9:16 p.m. mith612 New Reader

    The idea is you can multiply any one part of an equation by 1 and it doesn't change the equation.

    In this case you multiply 1/2(s-b) by (s+b)/(s+b) and 1/2(s+b) by (s-b)/(s-b)

    you now have (s+b)/2(s^2 - b^2) + (s-b)/2(s^2 - b^2)

    which is the same as (s+b+s-b)/2(s^2 - b^2)

    you can probably get it from there

  • CamaroKeith

    April 27, 2009 9:19 p.m. CamaroKeith New Reader

    Okay, I figured it out, I think.......

    when you multiply the denom of the one you have to multiply the num of that one also thus you wind up with....

    [(s+b)/s^2-b^2] + [(s-b)/s^2-b^2] = (s+b+s-b)/(s^2-b^2)

    The b terms in the num cancel and you are left with 2s/s^2-b^2

    I think that's how it works.

    Like I said, my nerves are just getting frazzled

  • mith612

    April 27, 2009 9:21 p.m. mith612 New Reader

    Bingo, you got it.

  • CamaroKeith

    April 27, 2009 9:22 p.m. CamaroKeith New Reader

    mith612 wrote:

    The idea is you can multiply any one part of an equation by 1 and it doesn't change the equation.

    In this case you multiply 1/2(s-b) by (s+b)/(s+b) and 1/2(s+b) by (s-b)/(s-b)

    you now have (s+b)/2(s^2 - b^2) + (s-b)/2(s^2 - b^2)

    which is the same as (s+b+s-b)/2(s^2 - b^2)

    you can probably get it from there

    Yep. Thanks. For the life of me could not think of this.

  • Grtechguy

    April 27, 2009 9:37 p.m. Grtechguy SuperDork

    yeah....................

  • aussiesmg

    April 27, 2009 9:43 p.m. aussiesmg Dork

    42..........oh wait

  • confuZion3

    April 27, 2009 11:38 p.m. confuZion3 Dork

    Miata. Isn't the answer Miata? Or E30? That's kind of a number.

  • thatsnowinnebago

    April 28, 2009 12:56 a.m. thatsnowinnebago HalfDork

    P71!!

  • spin_out

    April 28, 2009 12:23 p.m. spin_out New Reader

    Oooo Math fun. Can we have another?

  • billy3esq

    April 28, 2009 2:40 p.m. billy3esq Dork

    I think this problem was mostly bs.

    I can't believe I was first with that line.

  • John Brown

    April 28, 2009 2:48 p.m. John Brown SuperDork

    Morons.

    The answer is Mx5

  • CamaroKeith

    April 30, 2009 9:54 p.m. CamaroKeith New Reader

    billy3esq wrote:

    I think this problem was mostly bs.

    I can't believe I was first with that line.

    Actually, differential equations is bs

  • EricM

    May 1, 2009 10:31 a.m. EricM HalfDork

    CamaroKeith wrote:

    billy3esq wrote:

    I think this problem was mostly bs.

    I can't believe I was first with that line.

    Actually, differential equations is bs

    (N-M) (M-N) What is so hard about that?

    I loved DifeScrew after I ahd to take Transfermation of Linear Maticies.

  • pinchvalve

    May 1, 2009 10:39 a.m. pinchvalve SuperDork

    Uhhhhh, Miata?

  • John Brown

    May 1, 2009 12:39 p.m. John Brown SuperDork

    Ketchup

    John Brown wrote:

    Morons.

    The answer is Mx5

 
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