Random do my math homework for me thread

[nivlakian]

Hit "Thread Tools" which should be at the top right of the first post. Go to subscribe to this thread, then there is a drop down box for "Notification Type" and choose the one that says "instant notification by e-mail" or something of that sort.

[Woozie]

It worked. Thanks. I don't think I would have ever figured that out on my own lol. Now I just need to register my school email with BG since I check that one at least once per hour.

[Blubbartron]

I'm pretty sure I was allowed to use induction in proofs over the reals, but then again, I didn't go to the greatest university... If I had to take a stab at it, I would say the reason you can get away with it is the inductive hypothesis. You assume something is true for a particular *generic* X, and prove it's true for X + 1. X + 1 is to make the algebra easy, but X itself could be anything within the set that is appropriate for the question.

Granted, your way is the easy way, and I simply wasn't thinking. I had been awake for well over 24 hours, and my brain was shutting down.

[zoobernut]

This class is going to kick my ass. I haven't taken a proof based math class in years so I really need to get into that mind set. I am used to regular math classes. I will probably be bugging you guys more soon.

[Quicklet]

I'm pretty sure I was allowed to use induction in proofs over the reals, but then again, I didn't go to the greatest university... If I had to take a stab at it, I would say the reason you can get away with it is the inductive hypothesis. You assume something is true for a particular *generic* X, and prove it's true for X + 1. X + 1 is to make the algebra easy, but X itself could be anything within the set that is appropriate for the question.

Granted, your way is the easy way, and I simply wasn't thinking. I had been awake for well over 24 hours, and my brain was shutting down.

I'm not sure that would extend the proof over the reals, unless you can show that your generic X can be any real number within an interval that's at least of length 1, and then you would either have to show that this interval could be arbitrarily large in the negative direction (so that you could always prove the case for an infinitely large negative number), or else you would have to consider cases of X - 1. I'm not a mathematician, but I suspect there are better, more general methods of doing proofs over the real numbers.

[Woozie]

One of the issues that is immediately noticeable is the fact that the real numbers aren't well-ordered. If we want to show that some property holds over the natural numbers, we usually start with 1 (the lowest natural number) and show that it works for everything above.

So in this example, we can prove that if it works for a generic x, it works for x+1. But in induction, that's not enough. You also have to prove it in some initial case (for example, in induction you typically prove that it works for initial P1 case, then prove that if it works for Px, it also works for P(x-1). How would we choose our initial case in this example? If I choose my initial case to be the P0 case, then we still haven't proven it for (0,1). If we choose .5 for our base case, we still haven't done (.5,1). There's no initial case we can choose that would allow us to prove our property for the entire set).

Even if our set was (-infty,1], we would still have a problem. If we proved P1 and then proved Px => P(x-1), we're still only going to have proven P for {1,0,-1,-2,...}.

Px => P(x-e) for any positive e it would work. Though I'm not sure about that because I'm kind of zoned out on sleeping pills and cannot think clearly at the moment.

I think quicklet's way with intervals could work too. If you prove it on, say [0,1), and then prove [n,n+1) => [n-1,n). It works in this case because the number of sets you need to prove your claim for is countable (e.g. Pn = [n-1,n) for every natural number n).

[Ferion]

I found this write up by a professor from the University of Georgia about "Real Induction." I only read the first two or three pages though so I don't know how sound his logic is. I was never a huge fan of pure mathematics, but I'm sure at least Woozie will find it slightly interesting.

http://www.math.uga.edu/~pete/realinduction.pdf

Edit: Based on my quick read of the first couple pages I'm not sure if he's just trying to show that with the right assumptions you can do anything with math, or if he's actually trying to show/prove that you can use induction over the reals.

[Cream Soda]

Working on some genetics homework, this one should be easy but I'm lost with it, so if I could get an explanation rather than just an answer, it'd be much appreciated.

What is the probability of a family with six children having three boys and three girls?

Basically, what I understand is each child has 1/2 chance to be male or female, and I want to say well, 6 kids 50% chance to get 3 males 3 females, but it seems too simple @.@ and I know I'm missing something else.

Edit:This is for genetics, so will have to be math that can be done by hand, so statistics formulas are out.

For example, the next question, which I was able to solve

If three differently colored dice are rolled at the same time, what is the probability that a 6 will be the outcome on each one?

Each one has 1/6 chance so

1          1           1             1
--  x     --    x     --     =     --
6          6           6            216

[Mellema]

Hint for the first question: Pascals Triangle.

Edit: Didn't feel like typing everything out on my iPad, so now that I'm home I'll give a better explanation.

With 6 children there are 64 possible outcomes (2^6). If you draw out (or look up) Pascal's Triangle, the sixth row is 1,6,15,20,15,6,1. So the probability of 3 boys and 3 girls is 20/64 simplified to 5/16 or 0.3125.

[Blubbartron]

For the 3 boys/3 girls problem: http://en.wikipedia.org/wiki/Bernoulli_trial (define success as male, though it's equivalent to say female since the numbers are equal in this case)

There's no way to not use a "statistical formula" that doesn't require a retarded amount of work. I suppose you could crank out every permutation of genders for 6 children, but it would get super tedious, super fast. Bernoulli isn't exactly a super complicated formula, and depending on the level of the class, it could be assumed it's known.

Hint: this question is exactly the same as asking what the probability is of tossing a coin 6 times and getting exactly 3 heads. If your professor really wants you to do it by hand with n = 6, he's a sadist.

[Woozie]

The way I would solve this problem is I'd first figure out the probability of getting 3 boys and 3 girls in a particular order. For example, I'd find the probability of getting three boys first and then three girls.

Since the order of the children doesn't matter, I would then multiply my answer by the number of arrangements of three boys/three girls there are.

If I were to flip a coin 10 times, what's the probability of getting 5 heads and 5 tails? Well, let's consider the scenario in which I get 5 heads in a row and then 5 tails in a row. Each roll has a 50% chance of getting what I want, so there's a (1/2)^10 chance of me getting that exact result. But if I get 5 heads and 5 tails in a different order, I'm still getting what I want. So now I multiply this by the number of arrangements there are of 5 heads/5tails.

If I were explaining the possible arrangements to a class, I'd draw 10 boxes or lines

_ _ _ _ _ _ _ _ _ _

Then explain that I have to choose where to place the 5 heads. For example

_ H _ _ H H _ H _ H

After choosing the heads, there's only one way to arrange the tails (they have to fit into every blank). So this boils down to me choosing 5 places out of 10 to put the H's. So the number of arrangements would be 10 choose 5 (if you don't know what that means, just google "10 choose 5". Google will show the answer and will also have a link to the wikipedia page explaining combinations. But if you're in a class where you're solving problems like this, it's safe to say you're already familiar with these types of problems).

Also note that this problem is nothing more than the binomial distribution. So if you want more details about how your problem would be solved, you could google "binomial distribution" and see the explanations that are given. I'm willing to bet that there's a video on youtube that explains this in detail.

http://en.wikipedia.org/wiki/Binomial_distribution

If you follow my reasoning for the heads/tails problem, you should get [(1/2)^10]*[10!/(5!5!)]~.24609

If you follow the wikipedia formula for a binomial distribution (we can arbitrarily choose "heads to be success, in which case we want to know the probability of getting 5 heads out of 10 flips. So p=1/2, k=5) you get

[(1/2)^5]*[(1-1/2)^5]*[10!/(5!5!)], which is clearly the same thing I got. So if my explanation makes sense to you, use that same reasoning in your problem. If it doesn't, search "binomial distribution" in youtube or google and then apply the formula (arbitrarily choose either "boys" or "girls" as your "success" and find the probability of getting exactly 3 successes in 6 experiments).

Edit: I know you said statistical formulas are out. The teacher probably expected you to reason our your answer the way I did to get your result. However, the derivation for the formulas Blubbartron and I posted are done simply by the reasoning-out processes that I described above, so watching the youtube videos on the Binomial distribution would still help you understand how to use these problems, even without memorizing a bunch of distributions. Honestly, for simple distributions like the binomial one, it's better to just understand the reasoning and apply it to each problem than to memorize the formula anyways.

[zoobernut]

I need help with this problem if anyone has an idea. Given x is an element of the real numbers and x(sub n) is greater than or equal to zero and x(sub n) approaches x as n goes to infinity (limit) prove that the square root of x(sub n) approaches the square root of x as n goes to infinity. I found a theorem that allowed me to prove it in the opposite direction but I can't figure out how to go from x(sub n) to the square root of x(sub n).

[Niiro]

Granted this is a chemistry question, but the issue I'm having is mathematical in nature:



30 + 70 ≠ 100

[Blubbartron]

N2O4? The real question is why it's accepting 30% as correct for the Nitrogen component.

edit: I bet the person who made the question decided to accept any number beginning with 3, and then any number beginning with 6 on the second field, because trying to get a numerical answer equivalent to the fractions 1/3 and 2/3 is retarded if you don't specify a level of decimal precision.

double edit: herp derp, % composition is about % of mass, I can't math.

triple edit: I may have been on the right track anyway. http://www.convertunits.com/molarmas...ogen+Tetroxide says the actual % composition for Nitrogen is 30.446%, which means the Oxygen portion is 69.###%.

[Niiro]

After saying fuck it and giving up it gives the correct answer as 69.55etc

The retardedness comes from the fact that it accepted 30.4 rounded down to 30 as correct (also accepting rounded answers in the first question) but wouldn't accept 69.5 rounded up to 70.

[Psion]

So, retaking a calculus class cause i bombed it the first time... and it's not being much clearer this time around. I've had issues with math starting with trig, and i barely squeaked by precalc. I feel the issue is that it's complicated, boring as fuck, and i can't concentrate and figure out which symbols and letters represent which. It's also difficult because there's a fuckton of new formulas to memorize and none of it feels intuitive, partly because it drags stuff from several different fields, of which over half i haven't even seen the light of day of in over a decade. The other issue of course, being its all fucking symbols and letters and oh hey, f'(x) can also be called dy/dx and like a billion other things and lets call x z, no wait lets call it t (seriously, FUCK YOU PROFESSORS USING THIS LETTER AS A VARIABLE), and all of it is counterproductive to learning it all.

Maybe it's me coming from chemistry where a variable means one goddamn thing and one goddamn thing only. M always means molality, mL always means milliliters, and so on. Yes, i know variables in math can technically be called anything. great, we get it. now stop doing it, because it's confusing the fuck out of me. Stick to a goddamn standard and leave my poor brain alone.

So, i'm hoping that maybe some of you know a video game thats fun and teaches trig/calculus in an effort to engage my brain better and have the material "stick". if i had actual images and pictures showing how x and y relate, something that shows x and y as actual things that i can picture and see how the mathematicians of years past got their formulas, then maybe i wont feel like they just made all this shit up in a fit of lunacy.

So anyone have suggestions on games or stuff for someone who's heavily visually oriented and cannot for the life of himself make heads or tails of numbers and letters and squiggly lines?

[Datonare]

Most active math-y thread so I'm gonna post my question here... I just got back from an elementary algebra test I'm sure I did well on, but the last question stumped me and I got really frustrated. It's over and done with now, but if someone could help me work through it for my own knowledge, I'd appreciate it.

Question was something like: Jon has 32 hamburger patties and 34 tomato slices left. He sells his hamburgers as either singles or doubles. A single has 1 patty and 2 tomato slices, a double has 2 patties and 1 tomato slice. In order for Jon to use up all of his patties and tomato slices, how many singles and how many doubles must he sell?

Chapter was on graphing linear equations and I'm assuming this is using the substitution/addition method, but I couldn't get the equation formed. Closest I got was 2x + y = and 2y + x = (where x was the patties and y the tomato) but I don't even know if I was on the right track. I tried plugging in 32 and 34s in the equation, and unless I did it wrong, kept getting fractions, which make no sense in the context of the question.

I'm sure this is easy for most math aficionados in here, but I'm still learning lol

[Byrthnoth]

x is the number of singles
y is the number of doubles
x + y*2 = 32 (one hamburger pattie per single, 2 hamburger patties per double, 32 patties overall)
2*x + y = 34 (two tomato slices per single, 1 tomato slice per double, 34 tomato slices overall)

x = 32 - y*2 (rearrange the first equation)
64 - y*4 + y = 34 (substitution)
30 = y * 3 (push numbers around)
10 = y = 10 Doubles

x + y*2 = 32 (second equation)
x + 20 = 32 (sub in your result)
x = 12 = 12 Singles

2*12 + 10 = 34 (works out)
12 + 10*2 = 32 (works out)

[Datonare]

I'm disappointed I wasn't able to work through it on the test, but that's how it goes. Thanks for the help

[oldoldman]

So I need help with my last homework question I passed over and just can't wrap my head around. Might be because of lack of sleep.

The question is, "What is the value of (AXB)^2 + (A*B)^2?" where the first is the cross product and the second is the dot product and A and B are obviously vectors. I know it has something to do with Lagrange's identity I just can't fucking figure it out. Any help is appreciated.