Can be proved that Cos(ix) is bounded?

I want to ask you, Is there any inequality for |cosh(x)|? I have read that cosh(x)<= e^(x^(2)/2).

Hello everyone!

I want to solve a pde and create a matrix. But unfortunately, an error is formed. 

Please, someone help me to remove that error.

Here, I am attaching a mapple file.

pde_solu.mw