Both solutions are great, but I don't understand why my calculations gives other solutions than yours.

Thanks a lot!

Thanks a lot!
Both solutions are great.

@Mariusz Iwaniuk 

I found coś takiego:

https://www.maplesoft.com/content/EngineeringFundamentals/9/MapleDocument_9/Laplace%20Transforms.pdf

If I understand it well eq 15 Time Domain Convolution says you can, but I do not know how to do it in the Maple.

It was my mistake. I made a bad substitution.

Thanks for help!

@one man 

I want to find 5 variables (Z1(s), Z2(s), Phi1(s), Psi2(s) and Psi1(s)) and this are only algebraic equations. "s" is a complex variable after Laplace transform.

1. How do we know that this is the Transcendental equation?

2. I only want to transform the equation system to designate one variable. I do it well?

@Rouben Rostamian  Thank you all for help. Now everything is clear to me.

@Rouben Rostamian  For me linear equation is when I don't have sin(x) or cos(x) in all equation.

Wat do you think about this in my example?

bla.mw

I don't understand something.

Why in these solution of the equation I still have nonlinearity?

Sorry, I forgot about that. 
I want linearize around 0 of psi(t) and phi2 = 0,2617.

And thank you all for suggestions.

So far, I have tried with this formula, but I don't known what I must to do with derivatives

TaylorApproximation(expression, [psi1, phi2] = [0, 0.26], 0)

I'll try it soon as possible.

Still nothing.
When I export full worksheet to RTF (490 MB) and I open it by Word then I see only pictures with equations. I need equations to modifying and copy them to other program (LabVIEW).
In HTML I see only headers, text and a lot of blank space

I have Word 2016. At the moment I'm doing the calculations and when i finish, I'll let you know if it works.

Edit.

This solution did not work. After pasting I have something like that: math_xmlns.pdf

The file only contains a transformation of the system of equations, but a very long equation. 

This is my worksheet in Maple 2016:

5_equations.mw

@Kitonum 

My worksheet is significantly more bigger. First I must use packages like: Physics or DifferentialAlgebra to designate equations like RD11, RD22 and DR33. If I use "solve" then there's an error. So i must copy last result.

@Kitonum Yes, it works. But in bigger application i have to use packages. The equations are only results of many steps. So to use procedure "solve" I must manually copy result of each equation and paste in another line. Then I must use "restart" to get final result. I'm right? Is there another way?