Solving a second order ODE using reduction of order

2 replies · 2K views · last reply
Bonnie
Messages
18
Reaction score
1

Homework Statement


Hi there, I have an assignment which involves using reduction of order to solve for a second solution to an ode (the one attached). However this is a method I am new to, and though I have tried several times, I'm somehow getting something wrong because the LHS and RHS are not matching up, that is, when I substitue in the solution I have found, the RHS does not equal zero as it should.

Homework Equations

The Attempt at a Solution


I have attached my working (Sides 1 and 2), if anyone could point out what I'm doing wrong it would be greatly appreciated, this is driving me nuts!
 
Attachments
  • Printed question A1.1: show that y1 = t^3 solves 2t^2 y'' - 5t y' + 3y = 0, then use reduction of order to find a second, linearly independent solution y2.
    Question.JPG
    8.4 KB · Views: 470
  • Handwritten derivation solving 2t^2 y'' - 5t y' + 3y = 0 by reduction of order with y2 = u t^3, reducing to a first order equation in u' solved by separation of variables, ending with u = C1 t^(-2/5) + C2.
    s1.jpg
    54.4 KB · Views: 513
  • Handwritten derivation on lined paper: y2 = u y1 = (C1 t^(-1/2) + C2) t^3, general solution boxed as C1 t^(3/2) + C2 t^3, then C1 = 1 and C2 = 0 giving y2 = sqrt(t), then a check substituting y2, y2' and y2'' into 2t^2 y'' - 5t y' + 3y, which simplifies to 5t^(3/2) ≠ 0?
    s2.jpg
    62.3 KB · Views: 476
According to wolfram your general solution is correct.

You do a blunt mistake in the check, you put ##y'=-\frac 1 2 t^{-\frac 1 2}##, the minus in front is not needed. It is clear that ##y'=\frac{1}{2} t^{-\frac 1 2}## for ##y=t^{\frac 1 2}##
 
  • Like
Likes   Reactions: SammyS
Delta² said:
According to wolfram your general solution is correct.

You do a blunt mistake in the check, you put ##y'=-\frac 1 2 t^{-\frac 1 2}##, the minus in front is not needed. It is clear that ##y'=\frac{1}{2} t^{-\frac 1 2}## for ##y=t^{\frac 1 2}##
Oh, that was dumb. Thank you!
 
  • Like
Likes   Reactions: Delta2