# variables

1. ### quartiles

Please I have a question about quartiles: Can I organize from lowest to highest cualitatives variables through a weight assigned to them? For example John 4 Alex 3 Mary 2 Bob 1 and so if i have a sample: 3 3 3 3 3 1 1 1 2 2 2 2 2 4 4 , can I find the quartiles yet I...
2. ### How to solve for two variables in a 3x3 matrix?

Hi. I have this question on my Pre-Calculus homework that honestly I have no idea what to do for. We never went over this specific type of problem in class (go figure) and I'm unable to find anything else helpful on the internet. The problem is to solve for the two variables in this 3x3...
3. ### limit functions of 2 variables

Hi, Are there any examples of limit functions where the lim(x,y) ->(inf,0) or even lim(x,y) ->(0,0) and 0<=f(x,y)<=1. Particularly, as y -> 0 regardless of x, f(x,y) -> 1? The easiest function is (x/y) however this is explosive where x>y and especially where y = 0. Are there any online...
4. ### Need Help With Change of Variables from Cartesian to Spherical Coordinates

Hello there! Cutting straight to the chase, I need help with the derivation best described in this video here @ 7:48: https://youtu.be/AjDSLq-Pzcs?t=7m48s By this point in the video, Adam Beatty has already established: x=r*cos(Φ)*sin(θ) , y=r*sin(Φ)*sin(θ) , z=r*cos(θ) It also makes sense to...
5. ### Minima and maxima a function with two variables

Given A=[-1,1]^2 , f:A-->R(real numbers), f(x,y)=x^3+x*y+y^3, min f(A) doesn't exist, max f(A)= 1/27 , in (-1/3,-1/3) that's local maxima. But how can i fiind f(A)? And when can i say if the local maxima(minima) is the global maxima(minima?
6. ### Looking for verification on a function and solving for different variables.

logb(CL) = e # solve for L be = CL logC(be) = L # solve for C be = CL logL(be)= C I'm pretty sure L is right but what am I doing wrong when solving for C? Preciate any help anyone can provide. Thx.
7. ### Probability density function of sum 3 dependent random variables?

Suppose we have s = x+y+z and x,y and z are dependent random variables. Can I use this approach to find probability density function of S? first find CDF of S: $F_{S}(s)=P(S<=s)=\int_{-\infty}^{+\infty}dx \int_{-\infty}^{s-x}dy \int_{-\infty}^{s-x-y}f_{X,Y,Z}(x,y,z)dz$ and then differentiate it...
8. ### Mixed random variables with conditional probability constraints

Can someone please look at this problem statement in the attached photo and then explain the approach to solve such a problem my main problem with this question is I don't know to to find the probability when given multiple random variables also how do you take into account the conditionality...
9. ### Complex variables Integration

Let $$C_1 = \{z : |z| = 1\},\quad C_2 = \{z : |z - 2| = 2\}, \quad C_3 = \{z = x + iy : 4x^2+(y+3)^2 = 4\}$$ be contours with CCW orientation. > Calculate $$\int_{C_n} \frac {z+1} {z^4-16} {d}z$$ for $n=1,2,3$ **Solution Attempt:** $z^4 - 16 = 0$ which means $z = 2i, -2i, 2, -2$...
10. ### For the system of equations check whether the 2 conditions in IMF theorem are true

For the system of equations below, check whether the two conditions in the Implicit Function Theorem are satisfied at point A = (x, y, t) = (1, 1, 0), where x and y are variables and t is a parameter. If yes, find the expression for &dx/&dt and evaluate it at A. EQ#1 xy2 − y = 5t EQ#2...
11. ### Clever version of separation of variables

I came across a very interesting method to "separate" variables in an eigenvalue equation. But I'm not quite sure it works as advertised. Here's the sitch. We have, as usual: H \Psi = E \Psi, where H is dependent on both radial and angular variables, so we expect \Psi to contain both radial...
12. ### Joint Distribution of iid Random Variables

Hi, Let X,Y,Z be independent, identically distributed random variables,each with density$f(x)=6x^5$ for $0 \leq x\leq 1$ and 0 elsewhere.I want to find the distribution and density functions of the maximum of X,Y and Z. Answer:-I know by integrating density function, distribution function can...
13. ### Marginal distributions (and marginal density), three variables

I would like some help with this exercise, because I'm not completely sure about the difference between the distribution function and the density function in this context, and there is no solution in my book so I would like to know if I'm correct or not, since it is a pretty important part of...
14. ### Finding the covariance of two random variables X and Y

I understand all the steps but i don't know where the marginal density function for g(x) and h(y) (highlighted in yellow) came from. Can someone explain?
15. ### Question on role of independent variables in inverse functions

Hi everyone. I have been trying to get my head around this statements for three days. Could someone please explain this in different wors or perhaps provide an example. for some reason the books explanation isn't clicking with me
16. ### Method Of Substitution with 3 variables.

Sorry for lack of intelligence if it doesn't meet the standards of this website, but I am only in grade 9 academic math, but I am pushing my territory further every day, while I was looking for puzzles online, I came across a puzzle for a 3D graph. This puzzle requires method of substituion...
17. ### Does the C-statistic increase as you add variables?

I just read an article that used the c-statistic and I've got a question. In regression analysis we use r-squared, and we know that it increases as the number of independent variables increases. In logistic regression models the goodness of fit is determined with the c-statistic. Does it also...
18. ### Basic system of linear inequalities in two variables question

I just wanted to make sure that with this particular problem, the designated independent and dependent variable doesn't matter. Problem: Farmer McGregor plants oats and wheat on his farm. For conservation purposes, he plants at least twice as many acres of wheat as oats. He can handle up to a...
19. ### Midpoint Reimann Sum in Two Variables

Formula: z = xy R = (x,y) = |\, 8 \leq x \leq 14, 4 \leq y \leq 8 Estimate the volume below the surface using Reimann sum (m = 3, n = 2) taking midpoints. The change in x would be 14-8/3 = 2 and the change in y would be 8 - 4/2 (9)(5)(2) + (11)(5)(2) + (13)(5)(2) + (7)(9)(2) +...
20. ### Reimann Sum Problem in Two Variables

Formula: z = xy R = (x,y) = | 8 \leq x \leq 14, 4 \leq y \leq 8 Estimate the volume below the surface using Reimann sum (m = 3, n = 2) taking upper right endpoints The change in x would be 14-8/3 = 2 and the change in y would be [tex8 - 4/2[/tex] (10)(6)(2) + (12)(6)(2) + (14)(6)(2) +...