- #1
kostoglotov
- 234
- 6
Homework Statement
Regarding the case where the auxillary (characteristic) equation has complex roots, we solve the quadratic in the usual way using [itex]i[/itex] to get the general solution
[tex]y(x) = e^{\alpha x}\left(C_1 \cos{\beta x} + i C_2 \sin{\beta x}\right)[/tex]
And the textbook shows
[tex]y(x) = e^{\alpha x}\left(C_1 \cos{\beta x} + C_2 \sin{\beta x}\right)[/tex]
without the imaginary number [itex]i[/itex] in the equation.
At first I just assumed that the [itex]i[/itex] has been subsumed into the constant [itex]C_2[/itex], but then what is happening when we solve an initial value problem of this form, and find that [itex]C_2[/itex] is actually a real number? Where has the [itex]i[/itex] gone?