Solving a Second Order Linear Differential Equation

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Discussion Overview

The discussion revolves around solving a second order linear differential equation of the form y'' - 2y' + 3y = 0, with initial conditions y(0) = -1 and y'(0) = (√2) - 1. Participants explore the process of finding the roots of the auxiliary equation and the general solution for the case of complex roots.

Discussion Character

  • Homework-related
  • Mathematical reasoning

Main Points Raised

  • One participant expresses difficulty in solving the differential equation and identifies the auxiliary equation as r^2 - 2r + 3 = 0, noting that the discriminant is less than zero, indicating complex roots.
  • Another participant provides the general form of the solution for the case of complex roots, stating that if the roots are of the form r = M ± Ni, then the solution is y = e^(Mx)(Acos(Nx) + Bsin(Nx).
  • There are questions about using the quadratic formula to find the roots, with participants suggesting that the roots are r1 = 1 + i and r2 = 1 - i, confirming the values of M and N as 1.

Areas of Agreement / Disagreement

Participants generally agree on the method of finding the roots using the quadratic formula and the form of the solution for complex roots, but the discussion does not reach a consensus on the complete solution process or the application of the initial conditions.

Contextual Notes

The discussion does not clarify the application of the initial conditions to the general solution, leaving some steps unresolved.

s7b
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Hi,

I'm having problems solving this equation;

y'' -2y' +3y =0 y(0)=-1 , y'(0)=(root 2) -1

I found the auxiliary equation r^2 -2r +3 = 0
and since b^2 -4ac is less than zero this the case where r1 and r2 are complex numbers.

This is as far as I get without getting stuck.

Please help me out if you know this.
Thanks :)
 
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For ay''+by'+cy=0

the auxiliary equation is ar2+br+c=0. If b2-4ac <0, such that the roots are in the form [itex]r=M \pm Ni[/itex]

then y=eMx(Acos(Nx)+Bsin(Nx))
 
To find R1 and R2 do you just use the quadratic formula?

So r1= 1+i
and r2=1-i
 
s7b said:
To find R1 and R2 do you just use the quadratic formula?

So r1= 1+i
and r2=1-i

yep..so [itex]r= 1 \pm i[/itex] i.e. M=1 and N=1
 

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