Math Is Fun Forum

  Discussion about math, puzzles, games and fun.   Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ • π ƒ -¹ ² ³ °

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#176 Re: Help Me ! » Sines » 2006-01-20 04:26:22

Plain old sin(x) ranges from 1 to -1 on the y axis. You want half of that, so start with y= (1/2)sin(x). Now just add 1/2 to shift it up:

y= (1/2)sin(x) + 1/2

#177 This is Cool » Math *IS* Fun » 2006-01-19 19:58:03

ryos
Replies: 19

"Pinky, what is 'Troz'"?
"Why, it's 'Zort' in a mirror, Brain. TROZ!"

I'm still not entirely satisfied with this, but I wanted to put it to the "is it obvious what it is without me explaining it" test.

#178 Re: This is Cool » Implicit Graphs » 2006-01-19 17:52:46

Heh. I just found it (the applet) and tried to run it. It didn't quite work (the applet size was too small). Funny, since it worked fine when they graded it.

Now to see what sort of state the program is in...

#179 Re: This is Cool » Implicit Graphs » 2006-01-19 17:01:09

Umm...Let's see. I think the source is on a CD somewhere, if I even have it at all.

As far as the app goes, I'd have to do a fair amount of work on it before it were usable by the general public (incomplete interface--that's the biggest pain in Java programming). I never did finish it, see. And, it's a Swing app, not an applet.

I could look at taking the applet I wrote for the original assignment (if I still have that code) and adding Suess mode in, plus a marquee zoomer. I don't know how well it would run inside a web browser. Plus, I haven't written Java in about 4 years...

You've piqued my interest; I'll look for it. If something does come of it, I'd happily release the code as open source. But, no promises.

#180 Re: Help Me ! » fractions » 2006-01-19 16:49:19

"Dale a tu cuerpo alegría, macarena..."

Ahem. 1/100 as a percent is 1%. Percent means "out of 100", so if you have any number divided by 100, then the numerator is the percent.

Of course, that's not one of your choices, unless "nh" is supposed to mean "not here," in which case I would pick that.

#181 Re: This is Cool » Implicit Graphs » 2006-01-19 07:28:57

I'm surprised you didn't mention this.

Fractal math makes my head hurt, but I love the images. One assignment for an intro to computer programming course I took years ago was to write a java applet to calculate and graphically display the mandelbrot set. Fascinated, after the course I extended the program be a real java application. It did custom color gradients, had a marquee zoomer as well as numerical inputs, supported multiple windows with multithreaded rendering, etc. I was quite proud of it. I never did get to finish it, though, and now, years later, I don't have the time.

One of the coolest graphical effects in the program was the result of a moment of insanity. In Java, you represent colors as 4 byte integers, with the ARGB channels in subsequent runs of 8 bits. Of course, in Java all integers are 4 bytes, which means that any integer at all can be interpreted as a color. The result of the mandelbrot calculations in this particular calculator was an integer, one per pixel. You can see where this is heading...

I thought it would be cool to see what happened when I plugged the mandelbrot result directly into the color representation. The result looked a lot like an illustration in a Dr. Suess book, so I called it "Suess Mode." Some of the zoomed-in pictures in Suess mode were really fantastic. I wish I had saved some.

#182 Re: Help Me ! » A tricky problem to get you all thinking... » 2006-01-18 14:54:37

That doesn't quite compute. Doesn't probability only apply to random situations? Pi isn't random, and neither, I presume, are sudoku grids. I mean, that's like saying, "What is the probability that 2 + 2 = 4?" It's 1 of course; we know it will always come out a certain way.

So, either there is a sudoku grid in the digits of pi we already know, or there isn't.

On the other hand, if pi really never ever repeats itself, then we can also be certain that a sudoku grid is bound to crop up eventually.

What's a sudoku?

#183 Re: Help Me ! » 2 Event Probobility » 2006-01-18 14:43:56

The total number of ways a paper/ink choice combination could come out is given by p*i. So, it's 42. You seem to know that already.

So, the chance of any one of those choices coming up is 1/42. You need to figure out the probability that two paper/ink choices will come out a certain way.

The choices made in one event to not affect the probability of any given choice coming up in a second event. So, the probability of the first event happening the way it did is 1/42, and the probability of the second happening the way it did is also 1/42.

I think that, to put them together, you multiply them. This comes out 1/1764, like you said. Your teacher appears to have simply multiplied by the number of events (2), giving 1/21. That would mean that, as you add more events, the likelihood of any given series of events coming out a certain way increases, which just makes no sense at all.

To see why, imagine flipping a coin. The probability that a certain face will come up is 1/2. If you want the same face to come up again, the chances are (1/2)(1/2) = 1/4. If you were to multiply by the number of events (2), you would get a probability of 1. This would mean that a coin, once flipped, *must* turn up the same face in all subsequent flips. This is clearly not the case, and if your teacher disagrees with you, ask him if he's ever flipped a coin before.

I mean, I could be wrong, of course. Anyone?

#184 Re: Help Me ! » Poisson distribution » 2006-01-18 14:22:28

Poisson? Isn't that french for "fish"?

Sorry, I don't have anything helpful to say. tongue

#186 Re: Help Me ! » Help... » 2006-01-16 19:37:54

"Eek! Crock brained teachers? Sometimes I'm really glad I was homeschooled...."

Not teachers. Theorists. Administrators. Curriculum writers. Higher-ups. You know, The Man. Even an amazing teacher can only do so much with the system (s)he's given.

Teachers sometimes, too. I'd say about half the time, actually.

#187 Re: Help Me ! » Help... » 2006-01-16 18:53:12

Hoo...umm...what kinds of stuff I did...well...I quit.

In the middle of my junior year, I couldn't take the inanity any longer and I quit. Read a lot of library books for a year or so, then went to college. I'm now studying Chemical Engineering and doing fine. smile

So I guess I'm the opposite of you; I grew up schooled and finished homeschooled.

But don't worry, a lot of people aren't like me. They loved high school for some reason. There's nothing to say you can't be one of them.

Don't worry about tests. Tests are a piece of cake, especially in High School. Just pay attention when your teacher's talking. They generally go over things so many times that it's hard not to remember them when you take the test.

With tests, fear is your enemy. Fear degrades your ability to reason and remember things. I'm sure you'll find before too long that there's really nothing to worry about anyway.

Being a homeschooler, you know how you learn best. High school will force you to learn how some crock-brained educational theorist thinks you should learn. They will try to make you work harder than you need to in order to learn the material. The trick is to somehow do their way your way, and not let the busywork get you down.

What am I talking about? I failed at that so dramatically that I'm not even sure if it's possible.

I'm trying to be reassuring. I really am. I wish you the best of luck and hope you're successful and stuff.

#189 Re: Help Me ! » Help!! Stupid Story Problems! » 2006-01-15 16:41:39

1. P + 1.25P + 1.4(1.25P) = 560 Kg

2.25P + 1.75P    4P = 560

P = 140 Kg.

O = 1.75P = 245.

2. Q = P( 1+r)
Q1 = 200( 1+0.06) = $212
Q2 = 212( 1+0.06 ) = $224.72

Q3 = 350( 1 + 0.0575 ) = $370.13
Q4 = 370.13( 1 + 0.0575 ) = $391.41

391.41 + 224.72 = 616.13

Sorry if I was cryptic. I'm feeling lazy tonight. smile If you need better explanation, I'll oblige.

#190 Re: Help Me ! » Mom Needs Help!! » 2006-01-14 19:42:18

Not quite. Fixed costs are sunk, so they don't change no matter how much the company produces (or doesn't). So:

C = (2900 + 45x) / x

Is the average cost.

#191 Re: Jai Ganesh's Puzzles » Problems and Solutions » 2006-01-14 16:12:47

I didn't check if this one has already been solved, but since irspow asked about it, I gave it a go.

#192 Re: Help Me ! » Moment of Inertia, Potential energy, Velocity Problems (2) » 2006-01-14 14:47:00

The potential energy in problem 1 is given by U = mgy. That's 20 kg * 9.8 m/sec² * 200 m = 39,200 J.

I looked up the moment of inertia for a disk; it's I = 1/2MR². So for this disk, I = 1/2 * 20kg * (0.2m)² = 0.4kg*m²

To find the angular acceleration α, you need the angle θ of the slope of the incline. Then, you can find the maximum angular velocity. Convert this velocity to kinetic energy, and subtract it from the total potential energy. The remaining potential energy was converted to linear velocity, which you can find by converting the remaining potential energy back into velocity.

Problem 2:

a)  I = 140.625 Kg * m².
b) I sort of neglected torque when I took physics. Someone else will need to answer, or you can ask your teacher.
c) I neglected Power too
d) What is the diameter of the drum?

#193 Re: Help Me ! » Please Help me in formulars » 2006-01-14 14:21:11

This is a substitution problem. Since r=2v, you can plug that into p=r/4: p = 2v/4 = v/2.

P is "in terms of" v because it's by itself, and the only other variable in the equation is v.

#194 Re: Maths Is Fun - Suggestions and Comments » Emoticons - Smilie Expressions » 2006-01-14 14:17:03

There actually is an option to turn of display of smilies in posts. It's there for people like me, who despise animated smilies...

#195 Re: This is Cool » Implicit Graphs » 2006-01-14 11:40:44

I used the "Grapher" program that comes with Mac OS X 10.4. Yes, the blue line is tanxy = 0.

It's possible that the squiqqlies are an artifact of the way the program calculates implicit graphs. Or of the resolution reduction - I had the resolution down to half (more and it got too cluttered and didn't look as cool).

Here are some graphs of just tanxy = 0 so we can see more clearly what's going on. I also turned the resolution all the way up this time.

The first one is zoomed out a bit, because it just looks cool. smile

2 is the default view. I turned off the axes so it's easier to see that the function itself has "axes." If you look really closely, you can see that they don't quite meet in the middle - they're 1/x-shaped bow thingies.

Note also that every other line in the graph is smooth, and the others are jagged. Not that they're random - they definitely have a pattern to them.

In the third, I showed the region that I would focus my zooming in on.

The fourth is zoomed waaayyyy in (note the labels on the axes; I exceeded their precision, so they all look the same). These graphs seem to possess an almost fractal ability to provide detail, even when zoomed infinitely in. Note also that a definite pattern has developed, and this pattern is unaltered no matter how far I zoomed in.

#5 is just an intermediate zoomed-out view.

I love to play with these sorts of things. I could spend hours just zooming and scrolling around, looking for interesting things.

#196 Re: Maths Is Fun - Suggestions and Comments » Emoticons - Smilie Expressions » 2006-01-14 07:29:28

Hey, and jU, could I ask you a favor? Would you mind changing your signature to use the url= tag to reduce your signature link to something like this: Visit jU's Pet

Here's the code:

[url=::snip::=.png]Visit jU's Pet[/url]

#197 Re: Maths Is Fun - Suggestions and Comments » Emoticons - Smilie Expressions » 2006-01-14 07:27:07

Aaaarrrrggghhh! Smilies...dancing....must...restrain...fist of death...

::deep breaths::

Ok. How hard would it be to add a profile option to turn off the display of the smilies below the post box? Well, maybe pretty hard, since you'd probably have to add a database field and all the headaches that entails. Maybe I can get used to them, but...but...D'oh!

#198 Re: Help Me ! » Algebra » 2006-01-14 07:18:20

1. Distribute the minus sign through: 8h - 3h - 2k. This becomes 5h - 2k.

2. 5(m=n)-(3m+2n)  --  The parentheses don't make sense here. I'm going to rewrite it as 5m = n - (3m + 2n). Now:

5m + 3m + 2n = n
8m = -n

Solve for either:
n = -8m
m = -n/8

#199 This is Cool » Implicit Graphs » 2006-01-14 07:04:21

ryos
Replies: 17

Sometimes I graph the weird functions we get in my Calculus class, and surprising things come out. These were cool enough to share. (They wouldn't reduce down to <100K without unacceptable quality losses. And, I'm too lazy to link to them all. smile)

The consecutive numbers are me zooming out from a frame of like -2.5 - 2.5 to a frame in the tens of thousands. Some of them aren't that great. If you're on a slow connection, #3 is my favorite. Oh, and "Out" was the product of zooming back in randomly with the marquee zoomer. I would have gone farther too, but after that one the program froze. neutral

The red line is cos(xy) = 0, the green is sin(xy) = 0, and the blue is tan(xy) = 0.

While I'm not entirely sure I want to know wink, there are some really brilliant people here who enjoy a challenge, so I pose it: can anyone explain what's happening with these graphs?

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