Diffeq Definition and 66 Threads

  1. J

    Diffeq review book suggestions?

    Hi, sorry if this is posted/answered all the time, but I need some book advice. Basically, I will be taking this course in the fall: And required prep knowledge for entering this course is: Now I've taken tons of Linear Algebra and Multivariable calculus, but I need brush up on...
  2. M

    Confused on how my professor did this last step, DiffEQ, 2nd OrdER

    Hello everyone! My professor was going over a problem real fast for the exam and now that i went over it again, I'm lost on how he did this last step. He is using a method called Abels Theorum. THe problem says: Find a second solution of the given differential equation: t^2y''+3ty' + y = 0...
  3. M

    Stuck on equating co-efficents DiffEQ

    I'm confused on how to equate coniffecents. What I'm doing is, finding a particular solution for just the polynomial then I'm going to find it just for the exponential and add them together rather then putting it all together and making it a mess, but I'm stuck when i try to add the...
  4. M

    Why Do I Keep Getting the Wrong Answer in My Differential Equations Problem?

    Look whos back! I ran into another problem, i redid the problem twice and i keep coming out with the same answer! here is what i have: http://img139.imageshack.us/img139/6205/lastscan5qw.jpg This is waht I submitted which was wrong...
  5. M

    Solve Separable DiffEQ: Find General Solution & Functions | Help Needed!

    Can't figure out this seperable diffEQ! :( Hello everyone 'ive been trying to figure out this easy looking Differential Equation and yet its wrong! weee! Here is the problem: http://cwcsrv11.cwc.psu.edu/webwork2_files/tmp/equations/58/6217226076d5fd259f53ad1e3ed4071.png has an implicit...
  6. F

    Where am I going wrong with complex eigenvectors?

    I'm having trouble with this problem. Actually I'm having trouble with all of this set of problems (when the eigenvectors are complex). I must not be finding these things correctly, because nothing is matching up with the book. Any help would be awesome. \vec {x}\,' = \left( \begin{array}{cc}...
  7. F

    Solving Nonlinear Differential Equations for Air Drag in One Dimension

    I'm working on this project that involves air drag. The model for the air drag is given as: \vec F_d = \frac{1}{2} C \rho A v^2 I'm using Newton's Second law in relation to this force and gravity (in one dimension) which yields: a = \frac{1}{m} \left( -mg + \frac{1}{2} C \rho A v^2...
  8. F

    DIFFEQ - Discontinuous Forcing Functions (should be an easy question)

    Ok, we just started this chapter, and I am slightly confused with one specific aspect of the info... I'll just go through an example, it's the best way to explain it IMHO. I have to find the Laplace transform of the following function. The table of transforms that I can use are (sorry about...
  9. M

    [DiffEq] First order Modeling Applications

    YATP - Yet Another Trainlike Problem Sailboats A and B each have mass 60kg and cross the starting line at the same time of a race. Each has an initial velocity of 2m/s. Obviously from this, m1 = m2 == 60kg and vo1 = v02 == 2 m/s. The wind applies a constant force of 650N to each boat and...
  10. F

    DIFFEQ - Method of Undetermined Coefficients

    Sup' all? Ok, I have a quick question (hopefully). I'm trying to use the method of undetermined coefficients, and I keep getting stuck at one specific spot in the method. I'm not exactly sure what I'm doing. Let me try and explain: The problem is given as: 2y''+3y'+y=t^2+3*\sin t Which...
  11. F

    Modeling Mosquito Population Growth and Predation

    Ok, I have this modeling problem that I cannot figure out how to setup. The problem is given: The population of mosquitoes in a certain area increases at a rate proportional to the current population, and in the absence of other factors, the population doubles each week. There are 200,000...
  12. V

    DiffEQ 2nd order series sol'n problem: (1 - x)y'' + y = 0, x0 = 0

    This problem is from section 5.2 in Boyce, DiPrima's Differential Equations 8th edition. (1 - x)\,y''\,+\,y\,=\,0 I get: 2\,a_2\,+\,a_0\,+\,\sum_{n\,=\,1}^{\infty}\,\left[(n\,+\,2)\,(n\,+\,1)\,a_{n\,+\,2}\,-\,n\,(n\,+\,1)\,a_{n\,+\,1}\,+\,a_n\right]\,x_n\,=\,0 Which leads to one...
  13. T

    Power series solutions to diffeq

    I am suppose to find the power series solutions to some diffeqs. y'=xy The method is to assume that y=\sum_{n=0}^{\infty}{c_nx^n} is a solution to the diffeq.Then since we can differenitate term by term we have \frac{d}{dx} \left[ \sum_{n=0}^{\infty}{c_nx^n}...
  14. T

    Having trouble with Laplace Transform for DiffEQ

    Hello everyone, well thus far in our introduction to Laplace Transforms I am understanding much of what is being shown, however I am having the unsatisfying task of having to solve the following DiffEQ, y^3-8y=\sum_{k=0}^{3}\delta(2t-k\pi), y(0)=0, y'(0), y"(0)=0 I am having a great...
  15. M

    What is the radius of the circular hole in the bottom of the water tank?

    A water tank has the shape obtained by revolving the parabola x^2=by around the y-axis. The water depth is 4ft at noon when a circular plug at the bottom of the tank is removed. At 1pm the depth of the water is 1ft. a)find the depth y(t) of water remaining after t hours b)when will the...
  16. M

    How can I solve this DiffEQ problem involving retirement savings and salary increases?

    I am having a lot of trouble solving this problem. I don't even know where to start. Any help would be greatly appreciated. A 30 year old woman accepts an engineering position with a starting salary of $30000 per year. Her salary S(t) increases exponentially with S(t)=30e^(t/20) thousand...
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