shit is so confusing to me

@ThisIsChris let me know if that doesn't make sense

if any other <@&387091385075105804> know how to matlab, I would greatly appreciate the help!

@Sam Southern - TN the second line, `b = length(v);` is changing the value of b

how do I set the length of the vector to b?

@Sam Southern - TN so first I would make a vector of 1..b, I'll call it powers, s

so
`powers = 1:b`

then

`v = a.^b`

now it's giving me the last one instead of the first one as the output

so [8]

instead of [2]

but not [2 4 8]

hmm I see, I'm at work now will have to check this out in a little while (unless someone else steps in 🙂 )

thanks for trying though, I do appreciate it

@Sam Southern - TN this works

The trick I had to remember was that a function that accepts scaler, if you plug in a vector, will return you a vector with the function applied to each entry

that, and making the vector 1...b is `1:b`

@ThisIsChris thank you, that works!

just got back from work, happy to see this finally work hahah

@Sam Southern - TN You're weclome! 😄

Whoever recommended Professor Leonard. Probably the best videos I've found for this. Much appreciated

@Deleted User that was @JC17-OR

@Deleted User My pleasure

I was wondering if someone could help me with a problem for my financial mathematics class?

<@&387091385075105804>

@Tycho Brahe @Zyzz you guys too may have some insight for @Deleted User ?

I'll go ahead and post a screenshot of the problem so people could see if they would be able to help.

@Deleted User What's the question? If you drop it here then when someone who can help comes on they can work on it

yeah perfect

Here are my notes. The example is supposed to align with how to do the problem, I just can’t seem to get the right answer.

Let me know if my notes can't be read.

I'm going to get some rest for tonight, but if anyone would still want to look at it and give me some guidance, I would greatly appreciate it. 😃

First, find future value:
FV = Principle\*(1 + rate\*time)
FV = 875*(1 + .1025 * 2)
FV = 1054.375

Then in one year there will be one year on the note left, and the bank is going to discount that at a 17.5% rate, so the discounted value the bank pays satisfies:
FV = DV * (1 + .175 * 1)

Plugging in the value for FV from before:
1054.375 = DV * (1.175)

Dividing both sides by 1.175 we get:

DV = 897.3404255319 = 897.34

So the holder of the note went from 875 to 897.34 in one year, so he has his own future value calculation he can plug values into:
897.34 = 875\*(1 + rate_for_holder \* 1)

dividing both sides by 875 you get:

1.0255314286 = 1 + rate_for_holder
so rate_for_holder = 0.0255314286... ~~ 0.026
so the rate for the holder is 2.6%

@Deleted User

Thank you! @ThisIsChris I think I understand it much better now.

My pleasure! @Deleted User

Hey everyone I need some math help. I'm trying to do the final problem and I can't figure it out.

The best I've come up with is that the 2S-S argument only works for 2S -S, if you go above 2S-S to say 3S-2S, then it diverges to infinity. Also the r-value of 2 cannot be used in the geometric series sum equation as it is not between -1&1.

Any help is super appreciated.

If you talk about 3S you're just bringing more things in that you don't need.

when you do 2S-S you should have the same number of elements on both sides, or at least write it in the form of a sum

If you subtract these two sums, you should subtract the first from the first, the second from the second, etc.

So what you're saying is that the proof relies on ignoring standard rules of subtraction with equal terms.

It makes the assumption that you can subtract the 2+4+8+... of the S from the 2S while leaving the 1 untouched which negates the idea of infinity because it is adding terms to S that it is not adding to 2S to leave the 1 untouched.

When they subtract terms in the example, they're kind of cherry picking which to subtract first. It's not written in a strict mathematical way, so it flies under the radar. Imagine you said s = 1+1+1+..... You could say s -s = (1+1+...) -(1+....) = 1, yet s-s should be 0.

So you can point out that it's not written in a very precise way.

That makes sense. The proof isn't valid because it relies on a specific way to subtract the sums which doesn't follow mathematical rules.

Do I have that right?

@JC17-OR correct, the proof relies on the sum being the same if you are allowed to rearrange terms, but you are not guaranteed to be able to do that if the series is not absolutely convergent

Or you could say that they are using a different number of terms in each series in order to get the result that did. Which means that they didn't acttually double s, since s and 2s should have the same number of terms. If both series have the same number of terms, they end up with 2s-s = 2^N - 1, where N is the number of terms.

@JC17-OR You can also just prove that the series diverges just by making the terms rigorous:
Define S_n = sum i from 0..n of i^2
Then S = lim n->inf S_n

S_n you can compute explicitly, because it is a finite sum you can do:
2\*S_n - S_n = 2\*(n+1) - 1
i.e. S_n = 2^(n+1) - 1

so S = lim n-> inf 2^(n+1) - 1 = inf

That makes alot of sense.

Any thoughts on the 4th problem. My teacher hasn't been much help and my classmates are as lost as I am.

I figured I could take out the 1/sqrt(2pi) and have the integral e^(-x^2/2), integrate that and do the Taylor series that way, but that didn't work out.

@JC17-OR Unforunately I have to eat dinner now, but here is the lead, the derivative of F is f(x), but you know the taylor series for f(x), just take the taylor series for e^x and plug in (-x^2) where x is

So the taylor series for F is just the antiderivative of the taylor series for e^x * 1/sqrt(2pi) with (-x^2) plugged into x

Thanks for the help!

@JC17-OR You're welcome! Here's the full demonstration in case you want it:
F is the antiderivative of f so first find the taylor series of f:
f(x) = (1/sqrt(2pi)) * e^(-x^2)
taylor series for e^y is:
e^y = 1 + y + y^2/2 + y^3/3! + y^4/4! +...
plug in y=-x^2
e^(-x^2) = 1 - x^2 + x^4/2 - x^6/3! + y^8/4! -+...
so f(x) = (1/sqrt(2pi) * (1 - x^2 + x^4/2 - x^6/3! + y^8/4! -+...)
so F(x) = (1/sqrt(2pi)) \* (x - x^3/3 + x^5/10 - x^7/(7\*3!) + x^9/(9\*4!) -+...)

Does anybody have an idea for the power series from the given Taylor series?

@JC17-OR do you mean the radius of convergence?

because the taylor series *is* the power series

Anyway I forgot to mention the radius of convergence is infinity, because f(x) is a probability density function, so the integral of f(x) for x from -infinity to infinity is 1.

I'm dumb that's what I meant to say. I figured it out, thanks for all your help.

@JC17-OR You're welcome!

does anyone know anything about lognormal and weibull distributions?

<@&387091385075105804> ^^^

Need some help with a math problem @here

I have to solve a linear inequality problem:
A delivery driver makes $52 each day that she works and makes approx. $8 in tips for each delivery. If she wants to make $220 in one day at least how many deliveries does she need to make?

Isn't that just 220 = 52 + 8x

Is the $52 a base pay?

If so @Jacob is correct

Is is not (220 - 52) \ 8 = x

Oh jacob beat me to it. Jacob wrote the more proper expression tbh.

Do you solve for x or just leave it as that expression?

Solve for x

You solve for X but he got you started.

Since you get "approximately 8 dollars per tip' the answer will be "about" (whatever x is ) deliveries

Okay that makes sense.

Thanks. Your goy here can't do maths to save himself

Everyone has strengths and weaknesses. This one's pretty basic though. I used Kahn Academy alot in college when I had a foreign teacher who didn't explain things in an articulate manner.

I'm in a learning support math class since my ACT score wasn't high enough to be eligible for me to enroll in the primary math course required for my major.

So I have to take this class and then college algebra class and then hopefully I'm done

Kahn's really good if you prefer to learn with videos

52(base pay) + 8x(tips per delivery >or= to 220

8x >or= 168

x >or= 168/8 = 21 deliveries

At least 21 deliveries in a day

>she
Nice try Schlomo

@Freiheit - CA ?

Making women deliver stuff...sad

220-52=168
168/8=21
21 deliveries

She must live in Texas where tipped pay is $.38/hr or something

Anyone who has taken a class in Differential Equations, could you confirm if the answer in green makes sense?

This section is on series solutions for linear equations

@ButMomShesA300YearOldLoliVampire yes the way you solved it up to the green circle is correct. Now the question asks for you to find two linearly independent solutions. In the green circle you see that after you specify `C_0` and `C_1` that all the other coefficients of a solution are determined. So for one solution choose `C_0 = 1` and `C_1 = 0`, and for the other solution choose `C_0 = 0` and `C_1 = 1`. These solutions are linearly independent since no scalar multiple times the `C_0` and `C_1` of one solution will ever give you the `C_0` and `C_1` of the other solution.

@ThisIsChris Thanks a ton!