1
|
failsafe   United States. Sep 29 2008 19:42. Posts 1040 | | |
a high school girlfriend's dad was a computer programmer and when she was young he gave her a problem to solve. she never solved it, but she'd asked me my freshman year of college and i couldn't solve it... then yesterday it popped back into my head because i had an intuition about what the problem represented, yet even with some more math training i still haven't been able to make the connection and solve the problem!
so anyway the problem is simple:
there are two bugs... the first bug is crawling a long the x-axis and the second bug is crawling along the y-axis. the first bug starts at the origin and heads toward 1 on the x-axis. the second bug starts a 1 on the y-axis and heads toward the origin. the two bugs have a line between them and are moving at the same speed. what is the equation that describes the curve outlined by the series of lines drawn by the bugs.
so pretty much you've got f(x,y) = (x, 1-x) for your intercepts and the lines connecting the intercepts are tangent to a curve. the question is what is the equation of the curve?
presumably if i had any idea how to describe the sequence of lines i'd just integrate and know my answer but i'm instantly defeated. this is probably a ridiculously easy question because a guy at the local high school solved it instantly but i didn't know the guy and the girl who asked him on my behalf was a friend of a friend and the answer was never relayed to me
|
|
|
1
|
Jubert69   United States. Sep 29 2008 20:03. Posts 3191 | | |
What curve?, there is no curves by what your saying, its only line segments. |
|
|
1
|
failsafe   United States. Sep 29 2008 20:06. Posts 1040 | | |
the lines fill in the area beneath a curve. if all the lines that beetles drew were there at once there would be a curve over the area that the lines filled in. sorry for my vagueness |
|
|
1
|
TBB   United States. Sep 29 2008 20:18. Posts 781 | | |
y intercept wouldn't be 1-x because they are at different speeds. or am i missing something? |
|
|
|
1
|
Cro)Deadman   Croatia. Sep 29 2008 20:50. Posts 3943 | | |
u forgot the dead or alive part :O! |
|
|
|
4
|
Bigbobm   United States. Sep 29 2008 21:12. Posts 5511 | | |
| On September 29 2008 19:18 TBB wrote:
y intercept wouldn't be 1-x because they are at different speeds. or am i missing something? |
no youre adding something. the bugs are assumed to be traveling at the same speed as it isnt mentioned otherwise.
| On September 29 2008 19:03 Subaru wrote:
What curve?, there is no curves by what your saying, its only line segments. |
the line segment that connects the two points is a tangent line, which means only at one point does it touch the curve.
seems like a trick question imo. to have a function of f(x,y) = x, 1-x, where every point from [0,1] is a tangent line doesnt make sense unless the curve is a function of the bugs movement in which case id have to find a pencil and paper and i dont feel like doing that |
|
Its time to stop thinking like a bitch and think smart like a poker player - ket | |
|
|
4
|
Bigbobm   United States. Sep 29 2008 21:13. Posts 5511 | | |
oh if one bug is alive and other is dead this is ez |
|
Its time to stop thinking like a bitch and think smart like a poker player - ket | |
|
|
1
|
Graisseux   Canada. Sep 29 2008 21:50. Posts 474 | | |
Isn't it y = 1 - x ? I think you're really overthinking this |
|
| Last edit: 29/09/2008 22:05 |
|
|
1
|
spets1   Australia. Sep 29 2008 22:32. Posts 2179 | | |
|
|
|
1
|
thundza   United States. Sep 29 2008 23:04. Posts 2001 | | |
it's a quarter circle |
|
pausing stinger video to google ninja porn - myth | |
|
|
4
|
[vital]Myth   United States. Sep 29 2008 23:08. Posts 12159 | | |
yeah so the equation of the curve is (x - 1)^2 + (y - 1)^2 = 1 for 0 <= x <= 1 and 0 <= y <= 1 |
|
Eh, I can go a few more orbits in life, before taxes blind me out - PoorUser | |
|
|
0
|
eightfourO   United States. Sep 30 2008 00:05. Posts 820 | | |
i hate beetles so i take my shotgun and blow those fuckers up
=
problem solved.
kthxbai |
|
I am a god damn Rootin Tootin Shootin Cowboy!! | |
|
|
1
|
vegable   United States. Sep 30 2008 00:55. Posts 2453 | | |
Missing info: There was a pile of dead ethiopians at x=2?
|
|
|
|
1
|
thundza   United States. Sep 30 2008 01:32. Posts 2001 | | |
| On September 29 2008 22:04 thundza wrote:
it's a quarter circle |
actually... kinda a quarter circle, but not really. ask myth for more info. |
|
pausing stinger video to google ninja porn - myth | |
|
|
4
|
[vital]Myth   United States. Sep 30 2008 01:57. Posts 12159 | | |
woops, it's not a quarter circle, though it looks extremely close to it. talked to some better-at-math friends and it turns out that...
for time t = the time remaining that the bugs will continue to walk, and t in [0, 1], the slope of all the tangent lines is t/(t-1) and the y-intercept of all the tangent lines is t. therefore,
now, the curve defined by all these tangent lines is
so, to compute sup, we differentiate the tangent function with respect to t, getting
for which the critical points are at
or just 1 - sqrt(x) since t in [0,1]. so plug t = 1 - sqrt(x) into the curve and you will get
and the curve looks like this: |
|
Eh, I can go a few more orbits in life, before taxes blind me out - PoorUser | |
|
|
4
|
[vital]Myth   United States. Sep 30 2008 02:02. Posts 12159 | | |
also it looks from the graph like this function is not symmetrical about the y=x line but if you plug in some numbers, it is
for x = 0.81, sqrt(x) = 0.9, so y = 0.81 - 1.8 + 1 = 0.01, and when x = 0.01, sqrt(x) = 0.1, so y = 0.01 - 0.2 + 1 = 0.81
same works for (0.04, 0.64) and (0.64, 0.04), etc. |
|
Eh, I can go a few more orbits in life, before taxes blind me out - PoorUser | |
|
|
4
|
1
|
Day[9]   United States. Sep 30 2008 05:21. Posts 3447 | | |
well you can set up a parametric equation that...
damnit corwin -_- |
|
|
1
|
failsafe   United States. Sep 30 2008 08:23. Posts 1040 | | |
haha yeah my first thought too was just a quarter circle...
yeaaah so it turned out to be a least a little more complicated than i'd thought haha
awesome myth thanks =] |
|
|
1
|
failsafe   United States. Sep 30 2008 08:24. Posts 1040 | | |
|
|
|