ORDINARY DIFFERENTIAL EQUATIONS
1. Find the general solution of the following linear differential equations:
a. 2𝑥 2 𝑦 ′′ + 3𝑥𝑦 ′ − 15𝑦 = 0.
b. 𝑥 2 𝑦 ′′ − 7𝑥𝑦 ′ + 16𝑦 = 0.
c. 𝑥 2 𝑦 ′′ + 3𝑥𝑦 ′ + 4𝑦 = 0.
d. 3(𝑥 + 6)2 𝑦 ′′ + 25(𝑥 + 6)𝑦 ′ − 16𝑦 = 0 in the interval not containing 𝑥 = −6.
2. Find the series solution of the following linear differential equations:
a. 𝑦 ′′ + 𝑦 = 0 about 𝑥0 = 0
b. 𝑦 ′′ − 𝑥𝑦 = 0 about 𝑥0 = 0
c. 𝑦 ′′ − 𝑥𝑦 = 0 about 𝑥0 = −2
d. (𝑥 2 + 1)𝑦 ′′ − 4𝑥𝑦 ′ + 6𝑦 = 0 about 𝑥0 = 0
e. 𝑦 ′′ − 2𝑥𝑦 ′ + 𝑦 = 0 about 𝑥0 = 0
f. 𝑦 ′′ − 𝑥𝑦 ′ + 𝑦 = 0
g. 𝑦 ′′ + 𝑥 2 𝑦 = 0 with 𝑦(0) = 0, 𝑦 ′ (0) = 1
h. 𝑥 2 𝑦 ′′ + 𝑥𝑦 ′ + 𝑥 2 𝑦 = 0 with 𝑦(0) = 1, 𝑦 ′ (0) = 0
3. If 𝑃𝑛 (𝑥) denotes legendre polynomial of order n, prove the followings:
′ ( ) ′ ( )
a. 2𝑥𝑃𝑛′ (𝑥 ) + 𝑃𝑛 (𝑥 ) = 𝑃𝑛+1 𝑥 + 𝑃𝑛−1 𝑥 ,
′ ( ) ′
b. 𝑃𝑛+1 𝑥 = (𝑛 + 1)𝑃𝑛 (𝑥 ) + 𝑥𝑃𝑛 (𝑥)
′ ( )
c. 𝑃𝑛−1 𝑥 = −𝑛𝑃𝑛 (𝑥 ) + 𝑥𝑃𝑛′ (𝑥)
d. (1 − 𝑥 2 )𝑃𝑛′ (𝑥 ) = 𝑛𝑃𝑛−1 (𝑥 ) − 𝑛𝑥𝑃𝑛 (𝑥)
e. (1 − 𝑥 2 )𝑃𝑛′ (𝑥 ) = (𝑛 + 1)𝑥𝑃𝑛 (𝑥 ) − (𝑛 + 1)𝑃𝑛+1 (𝑥 )
f. Evaluate the following integrals:
1
i. ∫−1 𝑥𝑃𝑛−1 (𝑥 )𝑃𝑛 (𝑥 )𝑑𝑥
1
ii. ∫−1 𝑥𝑃𝑛 (𝑥 )𝑑𝑥
4. If 𝐽𝑛 (𝑥) denotes Bessel function of order n, prove the followings:
a. cos(𝑥 sin 𝜃) = 𝐽0 (𝑥 ) + 2 ∑∞
𝑛=1 cos(2𝑛𝜃 ) 𝐽2𝑛 (𝑥 )
∞
b. sin(𝑥 sin 𝜃 ) = 2 ∑𝑛=1 sin((2𝑛 − 1)𝜃) 𝐽2𝑛−1 (𝑥 )
𝑑
c. (𝑥 𝜇 𝐽𝜇 (𝑥)) = 𝑥 𝜇 𝐽𝜇−1 (𝑥)
𝑑𝑥
𝑑
d. (𝑥 −𝜇 𝐽𝜇 (𝑥)) = −𝑥 −𝜇 𝐽𝜇+1 (𝑥)
𝑑𝑥
e. 𝐽𝜇′ (𝑥 ) = 2[𝐽𝜇−1 (𝑥 ) − 𝐽𝜇+1 (𝑥)]
𝑥
f. 𝐽𝜇 (𝑥 ) = [𝐽𝜇−1 (𝑥 ) + 𝐽𝜇+1 (𝑥)]
2𝜇