The Simplify(expr) command converts the underlying trig functions in the given expression to radians-form, applies simplify, and converts back to degrees form.  Some additional care is taken to produce good results for expressions containing Int, Diff, and RootOf.  

This function is part of the Degrees package, so it can be used in the short form Simplify(..) only after executing the command with(Degrees). However, it can always be accessed through the long form of the command by using Degrees:-Simplify(..).

$\mathrm{with}\left(\mathrm{Degrees}\right)\:$

$\mathrm{expr}≔{\mathrm{sind}\left(x\right)}^2+{\mathrm{cosd}\left(x\right)}^2$

$\mathrm{expr}≔{\mathrm{sind}\left(x\right)}^2+{\mathrm{cosd}\left(x\right)}^2$

$\mathrm{Simplify}\left(\mathrm{expr}\right)$

$1$

The Degrees[Simplify] command was introduced in Maple 2021.

For more information on Maple 2021 changes, see Updates in Maple 2021.