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Second order differential equation

  • #1

Homework Statement


So I'm in pchem right now and I haven't taken dif eq (it's not required, but I wish I had taken it now!)

I am asked to solve this differential equation:

y''+y'-2y=0

Homework Equations



I know for a second order differential equation I can solve for the roots first. If there is one root then the solution will take the form y=c1erx+c2xerx

If there are two distinct roots I will get something like:
y=c1er1x+c2er2x

The Attempt at a Solution



I tried to find the roots

r2+r-2=0
r= -2 and r=1

So I get:

y=c1e-2x+c2ex

I am pretty sure this is correct (I checked to see if I got zero if I did y''+y'-2y and I did), but is there a way to find c1 and c2?
 

Answers and Replies

  • #2
SteamKing
Staff Emeritus
Science Advisor
Homework Helper
12,798
1,666

Homework Statement


So I'm in pchem right now and I haven't taken dif eq (it's not required, but I wish I had taken it now!)

I am asked to solve this differential equation:

y''+y'-2y=0

Homework Equations



I know for a second order differential equation I can solve for the roots first. If there is one root then the solution will take the form y=c1erx+c2xerx

If there are two distinct roots I will get something like:
y=c1er1x+c2er2x

The Attempt at a Solution



I tried to find the roots

r2+r-2=0
r= -2 and r=1

So I get:

y=c1e-2x+c2ex

I am pretty sure this is correct (I checked to see if I got zero if I did y''+y'-2y and I did), but is there a way to find c1 and c2?
Not unless you have some initial values to work with, such as y(0) = 0 and y'(0) = 0. You'll need two initial values to determine c1 and c2.
 

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