Homework help thread #2

Discussion in 'The Lounge' started by bubblegum, Jan 16, 2007.

  1. kdotc

    kdotc 안녕하세요빅뱅K-Dragon입니다

    internet beef =)
     
  2. Airree

    Airree Well-Known Member

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    I'm gonna try : D and well.. I've been everywhere..
     
  3. casshern

    casshern Well-Known Member

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    When people keep asking me useless questions. Kind of like what you're doing right now.

    I was thinking more along the lines of "genius".
     
  4. jm3

    jm3 Well-Known Member

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    2300? -rolleyes
     
  5. Airree

    Airree Well-Known Member

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    Sounds good. I'm beginning to like you.
     
  6. bubblegum

    bubblegum Well-Known Member

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    HAHA! why, then i should be in good shape -lol
    i'm starting to like u now :D

    uhm maybe, maybe not :D

    oh, what was your score then, if you don't mind me asking? :p

    lmao yeah that! can't believe I didn't kno what it was called. Stupid me -noclue

    gosh, that's so jacked up! :p

    btw, nothing math related but does anyone know what 3sf stands for in science?
     
  7. Airree

    Airree Well-Known Member

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    I'm not sure about 3sf but i know 3s is the name of an orbital of an atom. f is also another name of an orbital, but I'm not sure what 3sf together is.
     
  8. casshern

    casshern Well-Known Member

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    I'd rather you not.

    Why? She asked and I answered.

    3 Significant Figures.
     
  9. peachey

    peachey Well-Known Member

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    Great [​IMG] Hope everything's going well for you. [​IMG]

    Nope. Far from it actually. 2160 [​IMG] And that was after taking it a second time [​IMG]

    See above post.

    You may rest assured. I mean, surely Airree was just being sarcastic with that comment. [​IMG]

    Geniuses are often crazy. [​IMG]


    I have another problem though, but this one 'should' be easier because it's on the parabola. Unfortunately, I'm not good with geometrical problems.

    P is a point on the parabola x^2=4y
    The normal at P meets the parabola again at Q. The tangents at P and Q meet at T. S is the focus and QS=2PS

    a.) Prove that angle PSQ = 90 degrees
    b.) Prove that PQ=PT

    It's a parametrics question, which is an easier topic, but it's one that I struggle with for some reason.
     
  10. brown_bear

    brown_bear ☆‧° ☆﹒﹒‧ ☆ ﹒﹒‧☆‧° ☆

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    wow a recent thread dug out well done peachey -bigclap
     
  11. peachey

    peachey Well-Known Member

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    lol, only because I need help [​IMG]

    But yeah, I noticed that there has been an influx of old threads on the first few pages of several sections in the forum. What happened? [​IMG]
     
  12. brown_bear

    brown_bear ☆‧° ☆﹒﹒‧ ☆ ﹒﹒‧☆‧° ☆

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    we had an invader who was boosting his post counts well me thinks it was to download something but i dunno so he ran-sacked the lounge
     
  13. peachey

    peachey Well-Known Member

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    Oh, I see. Well, whatever it was he was attempting to download, I'm sure he has more than enough post counts to get it now [​IMG]
     
  14. brown_bear

    brown_bear ☆‧° ☆﹒﹒‧ ☆ ﹒﹒‧☆‧° ☆

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    ^ yeh he got his 200 and then stopped spamming
     
  15. Airree

    Airree Well-Known Member

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    That was a scary moment.
     
  16. casshern

    casshern Well-Known Member

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    a. Prove that PSQ = 90 degrees.
    The fuction of the parabola: y = x^2/4.
    -> The co-ordinate of P: P(xP, yP) with yP > 0 and yP = xP^2/4 (1).
    -> The co-ordinate of Q: Q(xQ, yQ) with yQ > 0 and yQ = xQ^2/4 (2).

    The co-ordinate of S is S(0,1), so we have:
    PS^2 = xP^2 + (yP - 1)^2 = (yP + 1)^2 <=> PS = yP + 1.
    QS^2= xQ^2 + (yQ - 1)^2 = (yQ + 1)^2 <=> QS = yQ + 1.

    Since PS = 2QS, we have: yP = 2yQ+1 (3).

    The fuction of the normal: y = ax + b with a < 0.
    Since the line y = ax + b is the normal of the parabola y = x^2/4 at Q(xQ, yQ), we have:
    a(xQ^2)'/4 = -1 <=> axQ/2 = -1 <=> axQ = -2 (4).

    P and Q belong to the line y = ax + b, so we have:
    yP = axP + b (5).
    yQ = axQ + b (6).

    From 1 2 3 4 5 6 we have the 6 variable system of equations:
    yP = xP^2/4
    yQ = xQ^2/4
    yP = 2yQ + 1
    axQ = -2
    yP = axP + b
    yQ = axQ + b
    =>
    yP = xP^2/4
    yQ = xQ^2/4
    yP = axP + b
    yP = 2b - 3
    yQ = b - 2
    xQ = -2/a
    =>
    yP = xP^2/4
    yP = 2b - 3
    2b - 3 = axP + b
    yQ = 1/a^2
    yQ = b - 2
    =>
    yP = xP^2/4
    yP = 2b - 3
    xP = (b - 3)/a
    b - 2 = 1/a^2
    =>
    2b - 3 = {[(b - 3)/a]^2}/4 (A)
    b = 2 + 1/a^2 (B)
    Replacing b in the equation (A) by (2 + 1/a^2) in (B) will give us:
    a = -1/2
    then b = 6
    xP = -6; yP = 9
    xQ = 4; yQ = 4

    => PQ^2 = 125.
    PS^2 = 100
    QS^2 = 25.
    Since PQ^2 = PS^2 + QS^2 = 125, according to the Pythagorean theorem, the angle PSQ = 90 degrees.

    b. Prove that PQ = PT.
    We already have the co-ordinates of P and Q. Defining the co-ordinate of T, and then calculating PT and comparing it to PQ will give you the desired result.


    God d@mn, that was a lot of work. I should be a part time math tutor. 25 bucks per hour unless you're a hot Asian chick, you can pay me other ways.
     
  17. onelove

    onelove Well-Known Member

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    ^lmao` dude..dat must have been a pain to type up`

    love`
    mon
     
  18. brown_bear

    brown_bear ☆‧° ☆﹒﹒‧ ☆ ﹒﹒‧☆‧° ☆

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    ^ nah me thinks he's used to typing that type of stuff if he knows how to solve them etc
     
  19. peachey

    peachey Well-Known Member

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    Anyway, I certainly hope I wasn't expected to be able to questions like that... just look at the amount of working [​IMG]
    I get the feeling it's not a standard parametrics question though, so hopefully that kind of stuff is just to "challenge" us as opposed to actually doing it in a 2 hour exam. [​IMG]

    Thank you for all your help, though, Geometry is really not my thing.

    Surely a few simple high school level math problems such as these should require very little effort from a "genius" such as yourself. [​IMG]
     
  20. qoo

    qoo Well-Known Member

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    ROARR I HATE PHYSICSS.. my teacher is a jerk who can't even teach.. he doesn't even check if we did our homework right =_=

    anyway.. i need help in phyiscs too!! ashdgaksfsldghaldjrhl;' so close to that 4.0 and this stupid class is keeping me from it DD:

    A child sitting 2.20 m from the center of a merry-go-round moves with a speed of 1.25 m/s. Calculate [a] the centripetal acceleration of the child, and the net horizontal force eserted on the child (mass= 25.0 kg)