# Simplifying a arc length problem

Simplifying an arc length problem

I have L= Int(-2..2) sqrt(16*cosh(4*t)^2+9*sinh(4*t)^2+9)

and can use Maple to simplify this to sqrt(25*cosh(4*t)^2)
but I just can't see how that is done. (or how to get maple to show me the steps!)

Can anyone help by showing the steps, including any trig substitutions/identities used?

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$$1+ \sinh^2 x = .....$$ so $$9 + 9 \sinh^2 (4t) = ..................$$?