@Kitonum Thanks for your answer and help. 

I want to solve it without inserting the parameters because the parameters are changing. And i need to create an Matlab skript with the equation. Any idea how i get the coefficient without inserting the parameters ? So normally i don't have these parameters. I just set some parameters to check the coefficients.

@Rouben Rostamian  What i am trying right now is : i am calculating with equation 3, 5 and 7 ca, cb, cc....This is normally not so hard because if i just have to pull ca in equation 3, cb in equation 5 and cc in equation 7 to the other side. 

Or am I wrong ?

and then i use the ca, cb, cc to calculate t1 t3 t5 and t7 ... and this is what i don't know how to do.

@Rouben Rostamian  First Thank you very much for the Help! and Thank you for the script it works really good. 

My Problem is that i want to calculate an analytical solution, so that i get an equation with the parameters. Because i want to implement the solution in a Matlab Skript and calculate an solution iterative with different Parameters. 

Is this possible to calculate an solution like this ? 

Again Thanks.

@tomleslie i added my script in the question :) so maybe some additional information about it ... normally there are 7 equations  and 7 uknowns --> so just t1 t3 t5 t7 and a b c ... the last equation eq7 doesn't have a b c ... so i first wanted to solve a b c with eq 1 3 and 5 and later than the other 4 with the other equations. --> the other variables are "given"

@tomleslie Thank you for your help.

I tried it with solve. The problem here is that if i run it ... nothing appens. Does this mean there is no solution ?