National Institute of Technology Tiruchirappalli
Department of Mathematics
Complex Analysis and Differential Equations (MAIR21)
I B.Tech ME-A Semester-II January 2025 Session
Problem Sheet-2
Find the Laplace transform of the following functions:
√ cos
√
1) t sin at 2) t cos at 3) ( t − 1 3
√ ) 4) √ t 5) f (t) = ⌊t⌋, the integer floor function
t t
sin t sin 5t
6) e−3t sin 5t sin 3t 7) e−t sin2 3t 8) e2t (3t5 − cos 4t) 9) sin t sin 2t sin 3t 10) t2 e−t cos t 11)
Z t Z t t t
1 − cos t −t e sin t
12) 2
13) e cos t dt 14) dt
t 0 0 t
Find the Laplace transform of the following functions:
2
√ 2 −t 3
(5t − 4 sinh 5t 2) (sin t − cos t) 3) sin( t 4) sinh 3t cos t 5) (1 + te )
1) 3 cosh
sin ωt, 0 < t < π/ω t, 0<t<π
6) f (t) = 7) f (t) = 8) t sin2 t 9) t2 cos at
0, π/ω < t < 2π/ω. π − t, π < t < 2π.
−t
sin t e sin t
10) 11)
t t
Find the inverse Laplace transform of the following functions:
3s + 7 1 − 7s 2s − 3 s (s + 2)2
1) 2) 3) 4) 5)
s2 − 2s − 3 (s − 3)(s − 1)(s + 2) s2 + 4s + 13 (s + 1)2 (s2 + 1) (s2+ 4s + 8)2
2 2
1 s +1 s s + 2s + 3 1 1
6) 3
7) log 8) cot−1 9) 2 2
10) sin
s(s + a) s(s + 1) 2 (s + 2s + 2)(s + 2s + 5) s s
Using convolution theorem, find the inverse Laplace transform of the following functions:
1 s s 1 s
1) 2) 3) 4) 5)
s2 (s + 1)2 (s − 1)(s2 + 1) (s2 + a2 )(s2 + b2 ) (s2 + 4s + 13)2 (s + 2)(s2 + 9)
Solve the following differential equations by using Laplace transform method:
1. y ′′ + 4y ′ + 3y = e−t , y(0) = y ′ (0) = 1.
2. y ′′ − 3y ′ + 2y = e3t , when y(0) = 1 and y ′ (0) = 0.
3. (D2 − 3D + 2)y = 4e2t with y(0) = −3 and y ′ (0) = 5.
d2 y dy dy
4. 2
+ 2 − 3y = sin t, y = = 0 when t = 0.
dt dt dt
d3 y d2 y dy 2 2t dy d2 y
5. − 3 + 3 − y = t e , where y = 1, = 0, = −2 at t = 0.
dt3 dt2 dt dt dt2
6. y ′′ + y = 0, y(0) = 2, y( π2 ) = 1.
d4 y
7. 4
− k 4 y = 0, where y(0) = 1, y ′ (0) = y ′′ (0) = y ′′′ (0) = 0.
dt
8. ty ′′ + y ′ + 4ty = 0, where y(0) = 3, y ′ (0) = 0.
9. y ′′′′ (t) + 2y ′′ (t) + y(t) = sin t, when y(0) = y ′ (0) = y ′′ (0) = y ′′′ (0) = 0.
10. (D2 + 1)x = t cos 2t, x = Dx = 0 at t = 0.
d2 y dy
11. 2
+ 5 + 5y = e−t sin t, where y(0) = 0 and y ′ (0) = 1.
dt dt
12. (D2 + ω 2 )y = cos ωt, t > 0, given that y = 0 and Dy = 0 at t = 0.