Here are the solutions for the given Laplace transform problems.
3.1 L{(e2t−1)2}
Step 1: Expand the expression (e2t−1)2.
(e2t−1)2=(e2t)2−2(e2t)(1)+12=e4t−2e2t+1
Step 2: Apply the linearity property of the Laplace transform.
L{e4t−2e2t+1}=L{e4t}−2L{e2t}+L{1}
Step 3: Use the standard Laplace transform formulas L{eat}=s−a1 and L{1}=s1.
L{e4t}=s−41
L{e2t}=s−21
L{1}=s1
Step 4: Substitute these transforms back into the expression.
L{(e2t−1)2}=s−41−s−22+s1
To combine into a single fraction:
=s(s−4)(s−2)s(s−2)−2s(s−4)+(s−4)(s−2)
=s(s−4)(s−2)s2−2s−2s2+8s+s2−6s+8
=s(s−4)(s−2)(s2−2s2+s2)+(−2s+8s−6s)+8
=s(s−2)(s−4)8
The final answer is s(s−2)(s−4)8.
3.2 L−1{s3e−3s}
Step 1: Identify the form for the Second Shifting Theorem.
The expression is of the form e−asF(s), where a=3 and F(s)=s31.
Step 2: Find the inverse Laplace transform of F(s)=s31.
We know that L{tn}=sn+1n!. For n=2, L{t2}=s32!=s32.
Therefore,
f(t)=L−1{s31}=21L−1{s32}=21t2
Step 3: Apply the Second Shifting Theorem, which states L−1{e−asF(s)}=f(t−a)u(t−a).
Here a=3 and f(t)=21t2.
So, f(t−3)=21(t−3)2.
L−1{s3e−3s}=21(t−3)2u(t−3)
where u(t−3) is the Heaviside step function.
The final answer is 21(t−3)2u(t−3).
3.3 L−1{s2+4s+133(s+2)}
Step 1: Complete the square in the denominator.
s2+4s+13=(s2+4s+4)+9=(s+2)2+32
Step 2: Rewrite the expression using the completed square.
s2+4s+133(s+2)=(s+2)2+323(s+2)
Step 3: Apply the First Shifting Theorem.
The expression is of the form F(s−a), where a=−2.
We know that L−1{(s−a)2+k2s−a}=eatcos(kt).
In this case, a=−2 and k=3.
So, L−1{(s+2)2+32s+2}=e−2tcos(3t).
Step 4: Include the constant factor of 3.
L−1{s2+4s+133(s+2)}=3L−1{(s+2)2+32s+2}
=3e−2tcos(3t)
The final answer is 3e−2tcos(3t).
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