Math Problem Statement

Find the inverse Laplace transform of following R(s); F(s) = 10 / [ s ( s + 2 ) ( s + 3 ) ^ 2 ]

Solution

To find the inverse Laplace transform of F(s)=10s(s+2)(s+3)2F(s) = \frac{10}{s (s + 2)(s + 3)^2}, we can use the method of partial fraction decomposition to express F(s)F(s) in a form where we can easily apply the inverse Laplace transform.

Step 1: Partial Fraction Decomposition

We start by writing: 10s(s+2)(s+3)2=As+Bs+2+Cs+3+D(s+3)2\frac{10}{s (s + 2)(s + 3)^2} = \frac{A}{s} + \frac{B}{s+2} + \frac{C}{s+3} + \frac{D}{(s+3)^2}

To find the coefficients A,B,C,A, B, C, and DD, we multiply both sides by the denominator s(s+2)(s+3)2s (s + 2)(s + 3)^2 to get: 10=A(s+2)(s+3)2+Bs(s+3)2+Cs(s+2)(s+3)+Ds(s(s+2))10 = A(s + 2)(s + 3)^2 + Bs(s + 3)^2 + Cs(s + 2)(s + 3) + Ds(s (s + 2))

Now we will solve for A,B,C,A, B, C, and DD by substituting convenient values for ss.

Solve for AA:

Let s=0s = 0: 10=A(0+2)(0+3)210 = A(0 + 2)(0 + 3)^2 10=18A10 = 18A A=1018=59A = \frac{10}{18} = \frac{5}{9}

Solve for BB:

Let s=2s = -2: 10=B(2)(2+3)210 = B(-2)(-2 + 3)^2 10=B(2)(1)210 = B(-2)(1)^2 10=2B10 = -2B B=5B = -5

Solve for CC:

Let s=3s = -3: 10=C(3)(3+2)(3+3)+D(3)(3)(3+2)10 = C(-3)(-3 + 2)(-3 + 3) + D(-3)(-3)(-3 + 2) 10=C(3)(1)(0)+D(3)(3)(1)10 = C(-3)(-1)(0) + D(-3)(-3)(-1) 10=9D10 = 9D D=109D = \frac{10}{9}

Solve for DD:

To find CC, we use any value of ss other than those previously used. Let's substitute s=1s = 1 into the equation: 10=A(1+2)(1+3)2+B(1)(1+3)2+C(1)(1+2)(1+3)+D(1)(1+2)10 = A(1 + 2)(1 + 3)^2 + B(1)(1 + 3)^2 + C(1)(1 + 2)(1 + 3) + D(1)(1 + 2) 10=A(3)(4)2+B(1)(4)2+C(1)(3)(4)+D(1)(3)10 = A(3)(4)^2 + B(1)(4)^2 + C(1)(3)(4) + D(1)(3) 10=48A+16B+12C+3D10 = 48A + 16B + 12C + 3D 10=48(59)+16(5)+12C+3(109)10 = 48 \left(\frac{5}{9}\right) + 16(-5) + 12C + 3\left(\frac{10}{9}\right) 10=240980+12C+30910 = \frac{240}{9} - 80 + 12C + \frac{30}{9} 10=26.666780+12C+3.333310 = 26.6667 - 80 + 12C + 3.3333 10=50+12C10 = -50 + 12C 60=12C60 = 12C C=5C = 5

Step 2: Inverse Laplace Transform

Now that we have the coefficients, we can rewrite F(s)F(s) as: F(s)=5/9s5s+2+5s+3+10/9(s+3)2F(s) = \frac{5/9}{s} - \frac{5}{s+2} + \frac{5}{s+3} + \frac{10/9}{(s+3)^2}

We can now find the inverse Laplace transform of each term separately using standard Laplace transform pairs:

  1. L1{5/9s}=591=59\mathcal{L}^{-1} \left\{ \frac{5/9}{s} \right\} = \frac{5}{9} \cdot 1 = \frac{5}{9}
  2. L1{5s+2}=5e2t\mathcal{L}^{-1} \left\{ \frac{5}{s+2} \right\} = 5 e^{-2t}
  3. L1{5s+3}=5e3t\mathcal{L}^{-1} \left\{ \frac{5}{s+3} \right\} = 5 e^{-3t}
  4. L1{10/9(s+3)2}=109te3t\mathcal{L}^{-1} \left\{ \frac{10/9}{(s+3)^2} \right\} = \frac{10}{9} t e^{-3t}

Combining these, we get: L1{F(s)}=595e2t+5e3t+109te3t\mathcal{L}^{-1} \left\{ F(s) \right\} = \frac{5}{9} - 5 e^{-2t} + 5 e^{-3t} + \frac{10}{9} t e^{-3t}

Thus, the inverse Laplace transform of 10s(s+2)(s+3)2\frac{10}{s (s + 2)(s + 3)^2} is: f(t)=595e2t+5e3t+109te3tf(t) = \frac{5}{9} - 5 e^{-2t} + 5 e^{-3t} + \frac{10}{9} t e^{-3t}

Do you want details or have any questions?

Here are some related questions you might find interesting:

  1. What is the inverse Laplace transform of 1s2+s+1\frac{1}{s^2 + s + 1}?
  2. How do you find the partial fraction decomposition of a rational function?
  3. What is the Laplace transform of teatt e^{at}?
  4. How do you compute the inverse Laplace transform of 1s(s+1)(s+2)\frac{1}{s(s+1)(s+2)}?
  5. What is the significance of the Heaviside function in Laplace transforms?
  6. How is the convolution theorem used in Laplace transforms?
  7. What are the properties of the Laplace transform that make it useful for solving differential equations?
  8. Can you provide an example of using Laplace transforms to solve a system of differential equations?

Tip: When performing partial fraction decomposition, always verify your coefficients by substituting back into the original equation to ensure accuracy.

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Math Problem Analysis

Mathematical Concepts

Partial Fraction Decomposition
Inverse Laplace Transform
Laplace Transform

Formulas

Inverse Laplace Transform formulas
Partial Fraction Decomposition formula

Theorems

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Suitable Grade Level

Advanced Undergraduate