- #1
ehabmozart
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Homework Statement
Solve the following DE
y'' + 8y' − 9y = 0, y(1) = 1, y'(1) = 0
Homework Equations
Homogenous DE with constant coefficients
The Attempt at a Solution
Well, i solved it normally using a CE and having
yH= c1 e^t + c2 e^(-9t) ..
y' = c1 e^t -9 c2 e^(-9t)
I then plugged in 1 in each of the above equation set from the homo. equation and its derivative and set that
c1 e^1 + c2 e^-9 = 1
c1e^1 -9c2 e^-9=0
I solved the eqns getting c1 =0.33 and c2= 810 getting my final homo. eqn as
y= 0.33 e^t + 810 e^ -9t
HOWEVER, this isn't the answer. The forum asks for my attempt NO? ... Well, the detailed answer just confuses me... Te fact that the I.C is y(0) and it is y(1) instead changes the procedure. I don't know why.. The book gives yh= k1 e^(t-1) + k2 e^-9(t-1) giving a note that c1=k1 e^-1 and c2= k2 e^9 ... They then write y'= k1 e^(t-1) -9 k2 e^-9(t-1)...
I am sorry for making this long but can any PATIENT person give me an explanation to this. I am pretty confused here and thanks in advance to whoever shows up with a good reply. I appreciate it a LOT! :D