- #1
toastie
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Homework Statement
y"+y=sinx
initial conditions: y(90 deg) = 3, y(45 deg) = 2
Calculate y at x = -1
Homework Equations
y=u+v
The Attempt at a Solution
I have gotten the following:
r^2 + 1 = 0 Therefore, r1=i and r2 = -i
u=(c1)cosx + (c2)sinx
v=Asinx + Bcosx
v'=Acosx - Bsinx
v"=-Asinx - Bcosx
-Asinx -Bcosx + Asinx + Bcosx - sinx = 0
everything cancels down to: -sinx = 0. Thus, v=0
Then I get,
y=(c1)cosx + (c2)sinx + 0
y(45 deg) shows that c2=2
y(90 deg) shows that c1=3
Thus, y=3cosx + 2sinx
y(-1) = -.06204
Could someone please let me know where I am making a mistake?
Thank you in advance!