AMATH 351 Homework 7: Series solution of ODEs
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AMATH 351 Homework 7: Series solution of ODEs
Exercise 1: First-order ODEs. By using the series expansion around zero for the solution: y(x) = 对 an xn , solve the ODEs:
1. y\ − y = 0. Hint: the solution is y(x) = a0 = a0 ex .
2. y\ = 2xy . Hint: the solution is y(x) = a0 = a0 ex2 .
Exercise 2: Hyperbolic cosine and sine. Find the general solution of
ODE
y\\ − y = 0, (1)
by using the series expansion of y(t) around t0 = 0:
∞
y(t) =工 an tn .
n=0
In your solution, use the following Maclaurin series for the hyperbolic cosine
cosh(t) =
and the hyperbolic sine
sinh(t) =
Exercise 3: By using the series expansion around t0 = 0, find the general solution of the ODE
y\\ + ty\ + y = 0. (2)
Hint: You should arrive to the closed form formulas for the series coefficients
( − 1)k ( − 1)k
a2k = 2 · 4 · 6 ··· 2k a0 , a2k+1 = 3 · 5 · 7 ··· (2k + 1)a1 .
Exercise 4: By using the series expansion around t0 = 0, find the general solution of the ODE
y\\ − 北y\ + y = 0. (3)
Hint: the solution is y(北) = a1 北 + a0 [1 − 北2 − 北2k] . Double
factorial n!! is the product of all integers from 1 to n with the same parity (odd or even) as n; e.g. 9!! = 9 · 7 · 5 · 3 · 1.
2023-05-20