- #1
jakobs
- 15
- 0
Homework Statement
This is my first big differential equation that I have solved by myself, and I wanted to see if it is correct done, or what I have done wrong with it.
Would really appreciate if somebody could take a look on it.
y''+6y'+8y=0
when y(0)=1 and y'(0)=0
The Attempt at a Solution
This is my solution
y''+6y'+8y=0
r2+6r+8=0
r=-3+- sqrt (9-8)= sqrt 1
r1= -2
r2= -4
y=Ce-2x+De-4x
y'=-2Ce-2x-4De-4x
y(0)=1 1=Ce0+De0=C+D
y'(0)=0 0=-2Ce0-4De0=-2C-4D
1=C+D
0=-2C-4D
I take 1=C+D and take -D on both sides so I get 1-D=C
I take 0=-2C-4D and take +2 on both sides so I get 2=C-4D
I now put in 1-D in it, and get 2=1-D-4D and that I can change to 3=-5D
I then take +5 on both sides and i get that 8=D
I go back to 1-D=C and I get that C=-7
I now take C and D and put them in the equation, so I get:
-7e-2x+8e-4x
Is this right, or have I made something wrong on the way?