Question: Maximizing a derivative in Maple

I have defined a function q(t) in Maple as:

q(t):=ln(cosh(t));

I then calculate it's 15th (!) derivative and assign it a name:

diffq(t):=diff(q(t),t$15)

 

I wish to maximize this function on the domain [0,50], so do the following:

maximize(diffq(t), t = 0 .. 50)

 

But this just throws out an expression rather than a particular maximum value.

I thought perhaps I need to use eval() on the derivative, so did the following:

maximize(eval(diffq(t),t=q),q=0..50)

 

However, this throws out a huge expression as well.

 

How would I use Maple to output the exact maximum value for this function?  I'm sorry if this is unclear, I am pretty new to Maple and also to this website, so please accept my apologies in advance but know that I am willing to learn!

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