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Reply 3680
[*] During the weekends, Eli delivers milk in the complex plane.

On Saturday, he begins at zz and delivers milk to houses located at z3,z5,z7,,z2013z^3, z^5, z^7, \cdots, z^{2013}, in that order.
On Sunday, he begins at 11 and delivers milk to houses located at z2,z4,z6,,z2012z^2, z^4, z^6, \cdots, z^{2012}, in that order.

Eli always walks directly (in a straight line) between two houses.

If the distance he must travel from his starting point to the last house is 2012\sqrt{2012} on both days, find the real part of z2z^2.
Reply 3681
I am doing some quantitative analysis on marginal costs and revenue, where I have to find the figure where marginal cost and marginal revenue are equal. I have
revenue = 720x - 4x^2
cost = 96-17x^2 + 560x

Ive got
marginal revenue = 720 - 8x
marginal cost = 560 - 34x

so when marginal cost = marginal revenue

720 - 8x = 560 - 34x
26x = -160
x = -6.15....

is it even possible to get a negative and what does this mean? at this point is it still maximum profit? which means you have to sell -6 units to make the maximum profit??

If someone could help today please
Reply 3682
Somebody who doesn't like milk has negged me. :rolleyes:
This crappy hand pointing downwards should be removed! :tongue:
Reply 3683
Original post by gff
Milk Delivery Problem


Here's a solution (I hope):

Spoiler

(edited 11 years ago)
Reply 3684
Original post by nohomo
Here's a solution (I hope):


It is a solution. :tongue:
Original post by nohomo
Here's a solution (I hope):

Spoiler

.


Slightly neater from this point to...

Spoiler

Reply 3686
A fair die is thrown four times and the number of times it falls with a 6 on the top, Y, is noted. Write down all the possible values of y.


Why is 0 the first answer?
Reply 3687
Original post by Farhan.Hanif93
Slightly neater from this point to...

Spoiler



That's a good improvement to the solution.

Does anyone have any more problems for people to solve?
Reply 3688
Original post by user
A fair die is thrown four times and the number of times it falls with a 6 on the top, Y, is noted. Write down all the possible values of y.


Why is 0 the first answer?


What result do you get if you roll 5 4 times?
Reply 3689
Original post by nohomo

Does anyone have any more problems for people to solve?

I have tons of fun problems to solve, but, unfortunately, not enough time. :colondollar: Help yourself. :tongue:
I know this is old but I just read the solutions by nohomo (and then the bit farhan posted); thought they were both a bit convoluted (algebra-wise) nearing the end (for me anyway)

Where nohomo says let z = a+bi

It's a lot easier to let z^2 = a+bi

and we have z21=1503|z^2-1| = \frac{1}{\sqrt{503}}
or (a-1)^2 + b^2 = 1/503

and since a^2 + b^2 = 1 then 2a-1 = 1 - 1/503 and then finally a = 1 - 1/1006

Sorry for the lack of latex; couldn't really be bothered :tongue:
(edited 11 years ago)
Is this just random questions?

5x0 = 0
Re-arrange.
5 = 0/0

seems legit
Original post by HypErTwisT
Is this just random questions?

5x0 = 0
Re-arrange.
5 = 0/0

seems legit


0/0 is an indeterminate. And the answer proves that 0/0 is infinity as it provides no solution, so there can be an arbitrary constant equal to this equation, as in this example:5.
Posted for Usycool:

When perpendicular lines meet, the product of their gradient is -1, right?

However, say if we have the lines y = 3 and x = 5.

The gradient of the y=3 in undefined, and the gradient of the x = 5 is 1.

So is this not an exception for the rule that perpendicular lines's gradients have a product of -1? Or is their another explanation for this?
Reply 3694
Original post by GreenLantern1
Posted for Usycool:

When perpendicular lines meet, the product of their gradient is -1, right?

However, say if we have the lines y = 3 and x = 5.

The gradient of the y=3 in undefined, and the gradient of the x = 5 is 1.

So is this not an exception for the rule that perpendicular lines's gradients have a product of -1? Or is their another explanation for this?


The gradient of the line x=5 is not 1.
Original post by Slumpy
The gradient of the line x=5 is not 1.


I only posted this for my friend not myself (so it has just been copied from what he has written to me). Can you please tell us what all the gradients are and if the prodyct of the gradients doesn't equal -1, then why!!
Reply 3696
Original post by GreenLantern1

The gradient of the y=3 in undefined, and the gradient of the x = 5 is 1.

:lolwut:
Original post by olipal
:lolwut:

I didn't agree with that euither - so I just decided to copy and paste what he said to me.


This isn't my writing but my friends; please just help him out as I am also intriguured by the answer!!!!!!!!!!
Original post by GreenLantern1
I didn't agree with that euither - so I just decided to copy and paste what he said to me.


This isn't my writing but my friends; please just help him out as I am also intriguured by the answer!!!!!!!!!!


Sorry, it was a typo, I meant the gradient of x = 5 is undefined and the y=3 has gradient 0. My mistake :facepalm:
(edited 11 years ago)
I wonder if I interrupted you guys.

I've asked this once in the Physics forum but I personally think that this is something about maths as well. I don't know if this is interesting but I guess it will be very challenging:

Pendulum we meet always have a rigid rod, what if it has a deformable string?

My approach is like this: I will set a Lagrangian equations like what people did in solving complex pendulum. The deformable rod will be treated as a (very) complicated pendulum with numerous bob with equal mass on it.

As string can't deform a lot (There is always curvature when you fold a rod), so my solution to the limit of deformation will be modifying the equation so that the bending of that particular point of the rod will have a very high damping, (like kθk \theta, k will be a constant depending on material and θ\theta is the bending angle to the normal of that particular point of the rod.)

So when I can set up an equation, I can gradually increase the points to a very large number and the motion of a pendulum will be simulated.

Anyway to add the work done against friction into Lagrangian mechanics? And any easier method to do this simulation?

-Agos

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