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  • Maths conversation

    E_net4 9 years ago
    This topic is to talk about maths.
    You can post maths problems, quotes and more.
    Example:
    cos Pi = -1

    But, of course, it is best to explain why.
    #
    Grim Reaper 9 years ago
    Seems sort of useless and boring.
    #
    LunaticNeko 9 years ago
        SIN COS TAN
    0? 0 1 0
    90? 1 0 inf

    I think this is quite a waste of time here. Anyone has problems? I do. It's more of physics than maths, though. It came from the older final exams at the school.
    Bus line #29 runs from Victory Monument to Rangsit Campus of Thammasart University. At the Victory Monument, there was 20 people on it. At Wat Samien, it picked up 20 people, and dropped 10. At Wat Don, it picked up 10 people and dropped 5. At Bangkok University, it picked up 10 people and dropped 15. And... close to the Thammasat University, the bus driver had to brake because there was a roadblock he didn't notice. He hit the brake at around 200 meters from the roadblocks.

    Assume that the coefficient of friction of the bus tires and the road while braking is 0.4, the bus has a mass of 4 ton, each person on bus have mass of 60 kilograms each, and the bus was running 60kph. How much does the whole bus weigh, and will it hit the roadblocks? Describe how.
    I didn't answer this question = =" However, for the sake of simplicity, I allow you to assume the g as 10m/s^2 or 9.81m/s^2... it's your call.

    HINT: There's more than one approach to answer this question!

    ANSWER: If your "g" was 9.81m/s^2, then the weight is 56898N, or if your g was 10.00m/s^2, then the weight is 58000N (the error was 1.9%). Still, no matter which value or formula/method you use, the answer is "It will not hit the roadblocks". If you need student-ready copy of the key that can be used against your Physics teachers, email me.
    #
    Idiota 9 years ago
    Problems? No, not really. I'm more of a person to help others with math problems.

    cos Pi = -1

    That's just too easy...

    what's the exact value of cos 1/3Pi? That's where it gets tougher, allthough it's still childsplay.


    I think only Amarth can shove math problems under my nose that make my eyes dazzle.
    #
    Amarth 9 years ago
    Bus line #29 runs from Victory Monument to Rangsit Campus of Thammasart University. At the Victory Monument, there was 20 people on it. At Wat Samien, it picked up 20 people, and dropped 10. At Wat Don, it picked up 10 people and dropped 5. At Bangkok University, it picked up 10 people and dropped 15. And... close to the Thammasat University, the bus driver had to brake because there was a roadblock he didn't notice. He hit the brake at around 200 meters from the roadblocks.

    Assume that the coefficient of friction of the bus tires and the road while braking is 0.4, the bus has a mass of 4 ton, each person on bus have mass of 60 kilograms each, and the bus was running 60kph. How much does the whole bus weigh, and will it hit the roadblocks? Describe how.
    Note, I'm completely neglecting approximation errors here. Since the mass of the bus is only given precisely up to 10^4 kg, it might be disastrous.

    There's 30 people on the bus (assuming the bus driver is counted in the inital 20). Total mass of bus: 4000 + 30*60 = 5800 kg.

    Kinetic energy of bus before braking: E = 0.5mv^2 = 0.5*5800*(60*1000/60/60)^2 = 805556 J

    Normal force between bus and ground: N = mg = 5800*9.81 = 56898 N

    Work done by friction: W = l*mu*N = 200*0.4*56898 = 4551840 J

    The bus will not hit the roadblocks. Correct me if I'm wrong, it's all a couple of years ago I did this.
    #
    E_net4 9 years ago
    I don't have such physics knowledge, none can do. :/
    ...Did you ever try to calculate the value of pi?
    Well, I did try, but it was useless...
    #
    Amarth 9 years ago
    "Thaimodz" said:
        SIN COS TAN
    90? 1 0 inf
    That is wrong, btw. tan(pi/2) is not infinity, it is undefined. Note that not even lim x->pi/2 tan(x) is infinity. The lim sup is, though.

    The reason is the same why lim x->0 1/x != inf. If I go towards 0 from the side <0, it goes towards -inf. Even better, if I go to 0 while alternating signs (for example, the series (-1/2)^n for n in the natural numbers), the limit does not exist. So, people, don't divide by zero plzkthx.
    #
    Madgamer 9 years ago


    How odd.

    My class is just picking up in trigonometry section and it is damn freaking hard. It's like English meets Math. You need to know both of 'em to actually get that thing to work, and when you do... total mess.

    I'm only good with numbers, not graphs and trigs stuff in particular.

    Also, deem this thread useless unless used for some type of mathematic code used for some type of weird computing language I wouldn't even know.
    #
    LunaticNeko 9 years ago
    "Amarth" said:
    "Thaimodz" said:
        SIN COS TAN
    90? 1 0 inf
    That is wrong, btw. tan(pi/2) is not infinity, it is undefined. Note that not even lim x->pi/2 tan(x) is infinity. The lim sup is, though.

    The reason is the same why lim x->0 1/x != inf. If I go towards 0 from the side <0, it goes towards -inf. Even better, if I go to 0 while alternating signs (for example, the series (-1/2)^n for n in the natural numbers), the limit does not exist. So, people, don't divide by zero plzkthx.
    Well, I already knew that, but the physics teacher always say "At least it sounds way cooler and easier to write than '0 1 0, 1 0 Undefined'."

    Hint : For the Physics problem, it's simple enough that you don't need to use the energies. Simple equations will do enough
    #
    Amarth 9 years ago
    "Madgamer" said:
    Also, deem this thread useless unless used for some type of mathematic code used for some type of weird computing language I wouldn't even know.
    Okay. Turing machines.

    If we can make a computer based on current technology (=deterministic calculations) that completely simulates our universe (however slow that'd be), we either cannot build a computer that solves minesweeper in polynomial time or none of our bank accounts and secure internet connections are safe.

    How's that for a mathematical result?
    #
    E_net4 9 years ago
    "Madgamer" said:
    Also, deem this thread useless unless used for some type of mathematic code used for some type of weird computing language I wouldn't even know.
    Every programming language uses Maths, and you may not know, but trigonometry is very important under some games.

    If we can make a computer based on current technology (=deterministic calculations) that completely simulates our universe (however slow that'd be), we either cannot build a computer that solves minesweeper in polynomial time or none of our bank accounts and secure internet connections are safe.
    I actually made a galaxy on my calculator...
    Kidding, it was just a 32x32 matrix with an integer representing the type of star.

    Lol@2D Galaxy With Stars Only
    #
    LunaticNeko 9 years ago
    Well, might consider this derailing serious talk, but it's all maths!

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    [13+ language]





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    #
    Anarion 9 years ago
    Thats great Thaimodz! The one about the graph was classic.
    #
    Anonymous1157 9 years ago
    There's another one on the website he linked to that says: "Find X." "Here it is!"
    #
    Madgamer 9 years ago
    I'm bored and I don't really know a lot of trigs so here's this one for ya:

    Typical mathematician in the good ol' catholic state: "Lord, give me a sine."

    And the lord said to John,"Come forth and you shall receive eternal life." But John came fifth and won a toaster.

    Go ahead, laugh

    Edit: California is now very F'ing hot. I think my mind was fried due to dehydration... Gah... What am I saying?
    #
    Idiota 9 years ago
    Lol Thaimodz, those are funny. Makes me remember someone doing a calculation to find X.

    And then a miracle occured!
    X = 6
    #
    Amarth 9 years ago
    "Idiota" said:
    Makes me remember someone doing a calculation to find X.

    And then a miracle occured!
    X = 6
    This one, perhaps?

    #
    Idiota 9 years ago
    yeah I was just throwing in a rough sketch of the situation. the real thing is justt brilliant.
    #
    LunaticNeko 9 years ago
    That reminded me of someone's problem solving... maybe like this...
    A student is trying to measure the flag pole of the school. When he stands 20m away from it, he can look up to the top of the pole with 30 degrees of angle. How high is the flag pole?
    And this is what his book looked like when I saw it one day...
    Let C represent the base of the flag pole, B for the student, and A for the top of the pole.
    Then a miracle occured?
    The flag pole must be 20sqrt(3) meters high. --- I told you to do it yourself.
    #
    Amarth 9 years ago
    Shouldn't that be 20/sqrt(3) m?

    If you can't even trust miracles anymore...
    #
    LunaticNeko 9 years ago
    No point. He will get it wrong anyways

    In fact, he had both trustworthy and untrustworthy miracles in his notebooks, workbooks, exams, ...
    #
    Idiota 9 years ago
    tan 30 = x/20
    x = 20 * (tan 30)
    x = 20 * 1/3 * sqrt 3
    x = 6.7 sqrt 3
    #
    LunaticNeko 9 years ago
    -0.25 from Idiota. Was it in radians or degrees? And another 0.25, you did the thing, yes, but our regulations here require that if you dare use decimals, we need 2 digits. And don't forget about the units. (well I ALMOST got that once)

    Oh, I forgot! -0.25 from Amarth as well, no sqrt's as divisor.

    In fact, when you get in doubt about trigonometry in Thailand, you only have to do one or more of the following and hope for miracle...

    1. Answer "1"
    2. Answer "0"
    3. Answer "Undefined"
    4. Answer "(one of the numbers) sqrt(2 or 3)", add fractions if you want
    5. If you need to be descriptive, draw a triangle and a unit circle.
    6. Write all those "sin^2 x + cos^2 x = 1" , etc etc that you know
    7. Assume and represent random stuffs
    8. Someone "randomed" in the choice part of the answer sheet, miraculously, he got around 50%...
    #
    Amarth 9 years ago
    "Thaimodz" said:
    -0.25 from Idiota. Was it in radians or degrees?
    Unless defined, it's in radians, always. Degrees are simply not used with trig functions, except on the very basic level where you still have the relationship with triangles, and then of course it's mandatory to say so. So Idiota's calculation is wrong.
    And another 0.25, you did the thing, yes, but our regulations here require that if you dare use decimals, we need 2 digits. And don't forget about the units. (well I ALMOST got that once)
    He said 20/3 right above it. Though, it's kind of strange to chop off 20/3 but not sqrt(3).
    Oh, I forgot! -0.25 from Amarth as well, no sqrt's as divisor.
    What a stupid and arbitrary rule. You don't have statistics I guess? Well, multiply numerator and denominator with sqrt(3), then, and you'll get the same thing as Idiota.
    #
    Idiota 9 years ago
    Sheesh dudes, you get what I mean. :p I was a bit bothered of how to write it down so I just wrote it in decimals for ease. I prefer doing calculations with hand. Only I can read my notes, but at least it goes a bit faster.
    #
    Murska 9 years ago
    "Idiota" said:
    I prefer doing calculations with hand. Only I can read my notes, but at least it goes a bit faster.

    The EXACT same thing goes for me.
    #
    LunaticNeko 9 years ago
    Yes, amarth. When we do that, we must multiply it. If it's exams made/held by other institutes, we must always answer with 2 decimal digits unless told otherwise.

    And all those $***s were just to make fun of some old-headed teachers, not to criticize you guys directly. (Someone got a zero because he forgot to write one of the lines!)

    Yes, only I can read my notes. If someone wants it and threatens for my life, then he's practically screwed
    #
    Murska 9 years ago
    It seems only I can also read my English. In the exam, there was only a single mistake. Everything else was the teacher not understanding the word properly etc.
    #
    E_net4 9 years ago
    And now, folks, I assume you're getting offtopic.

    Here's a damn-old-n-easy riddle, just to make you read it:
    7 is an odd number. How do you make it even?
    #
    Pete 9 years ago
    "E_net4" said:
    Here's a damn-old-n-easy riddle, just to make you read it:
    7 is an odd number. How do you make it even?
    Never heard of it, but I would guess you take away the s.
    #
    E_net4 9 years ago
    Yep, Pete, that's the answer.
    Have you seen the "There is an elephant in the way!"?
    #
    LunaticNeko 9 years ago
    Read it. Well, a friend (?) asked me when he saw it...

    "Hey, was that you back at the competition?"

    Yes, I admit I draw like that. But... = ="
    #
    E_net4 9 years ago
    We need more maths jokes, people! XD
    #
    Amarth 9 years ago
    "E_net4" said:
    We need more maths jokes, people! XD
    The standard one... Basic calculus knowledge required.

    f(x) = e^x and f(x) = c are walking in the forest. Suddenly, the constant function spots a differential operator. He shouts 'Oh no! If he sees me, I'll be reduced to nothing!" and he runs away. The exponential function goes towards the differential operator and says "I am not scared! You cannot change me, for I am f(x) = e^x!" The differential operator responds: "Hi! I'm df/dy!"

    Or, a more advanced one (complex analysis):

    Q: What is the contour integral of West Europe?
    A: Zero, because all the Poles are in East Europe! (or, more accurate, zero because all the Poles are removable )
    #
    E_net4 9 years ago
    Ouch. Couldn't get the joke.
    #
    Forum » Maths conversation
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