Common Laplace Transforms and Main Properties
Common Transforms.
(1)
1
L {1} (s) = , s > 0.
s
(2)
1
L eat (s) =
, s > a.
s−a
(3)
n!
L {tn } (s) = , n = 1, 2, ..., s > 0.
sn+1
(4)
b
L {sin(bt)} (s) = , s > 0.
s2 + b2
(5)
s
L {cos(bt)} (s) = , s > 0.
s2 + b2
(6)
n!
L eat tn (s) =
, n = 1, 2, ..., s > a.
(s − a)n+1
(7)
b
L eat sin(bt) (s) =
, s > a.
(s − a)2 + b2
(8)
s−a
L eat cos(bt) (s) =
, s > a.
(s − a)2 + b2
(9)
1
L {Hc (t)} (s) = e−cs , s > 0.
s
(10)
L {Hc (t)f (t − c)} (s) = e−cs L {f (t)} (s), s > 0.
For c > 0, the Heaviside function (or unit step function) Hc (t) in (9) and
(10) is the piecewise continuous function given by:
0, 0 ≤ t < c,
Hc (t) =
1, t ≥ c.
1
2
Some Properties of the Laplace Transform.
Suppose f and g are such that their corresponding Laplace transforms,
F (s) = L {f (t)} (s), G(s) = L {g(t)} (s)
exist, and let c, a ∈ R.
(1) (linearity)
L {f + g} (s) = F (s) + G(s), L {cf } (s) = cF (s).
(2) (translation)
L eat f (t) (s) = F (s − a).
(3) (transform of f 0 )
L f 0 (t) (s) = sF (s) − f (0).
(4) (transform of f 00 )
L f 00 (t) (s) = s2 F (s) − sf (0) − f 0 (0).
(5) (transform of f (n) , the nth−derivative of f )
n o
L f (n) (t) (s) = sn F (s) − sn−1 f (0) − sn−2 f 0 (0) − ... − f (n−1) (0).
(6) (derivative of the transform)
dn
L {tn f (t)} (s) = (−1)n F (s).
dsn