Hello,
in Mathematica I got an output like

(cosh sin sinh \[Eta]^2 \[Theta]^2 (-((-2 + cosh) \[Eta]^2) + 
   sin \[Theta]^2))/((cosh \[Eta]^2 - sin \[Theta]^2) (sinh \[Eta]^2 +
    sin \[Theta]^2)).

How do I have to interpret this expression? What can/must I do to get a reaable and correct output?
I used the following code:

t = (2*a^2*cosh (\[Eta])*sin (\[Theta])^2*
     sinh (\[Eta])^3/(cosh (\[Eta])^2 - sin (\[Theta])^2)^3 - 
    a^2*cosh (\[Eta])*sin (\[Theta])^2*
     sinh (\[Eta])/(cosh (\[Eta])^2 - 
         sin (\[Theta])^2)^2)*(cosh (\[Eta])^2 - 
      sin (\[Theta])^2)^2/((sin (\[Theta])^2 + sinh (\[Eta])^2)*a^2)
t;

FullSimplify[t]