Solve the following set of equations using Laplace Transforms y''+z′'−z′=0 y′+z′−2z=1−e^(−t)

Uriel Hartman

Uriel Hartman

Answered question

2022-11-05

Solve the following set of equations using Laplace Transforms
y + z z = 0
y + z 2 z = 1 e t
where y 0 = 0 , z 0 = 1, y 0  and  z 0 = 1 I've found that
L ( y ) = p L ( y ) y 0
L ( y ) = p 2 L ( y ) p y 0 y 0
L ( 1 e t ) = 1 p 1 p + 1
Which gives the set of equations
p 2 L ( y ) 1 + p 2 L ( z ) p 1 p L ( z ) + 1 = 0
p L ( y ) + p L ( z ) 1 2 L ( z ) = 1 p 1 p + 1
How to solve for y and z.

Answer & Explanation

andytronicoh4t

andytronicoh4t

Beginner2022-11-06Added 18 answers

You have the following system of equations in L(y) and L(z):
p L ( y ) + ( p 1 ) L ( z ) = 1 p + 1 p L ( y ) + ( p 2 ) L ( z ) = 1 p 1 p + 1 + 1
Subtracting the first and second equations we get
L ( z ) = 1 p + 1 ,
then substituting L(z) into the first equation we get
p L ( y ) + p 1 p + 1 = 1 p + 1 p L ( y ) = 1 p + 1 p 1 p + 1 p L ( y ) = 1 p + 2 p + 1 L ( y ) = 1 p 2 + 2 p ( p + 1 ) L ( y ) = 1 p 2 + 2 p 2 p + 1 .
Hence
y ( t ) = t u ( t ) + 2 u ( t ) 2 e t u ( t ) = ( t + 2 2 e t ) u ( t ) z ( t ) = e t u ( t )
with u the unit step function, i.e.
u ( t ) = { 0  if  t < 0 1  if  t 0 .

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