We have seen three kinds of parentheses used in Maple - ( ), { }, 
.
Each plays a different role.
bullistitem ( ) is used in expressions as in 
, or surrounds
the argument of a standard function as in 
or surrounds the
arguments of a Maple function as in
solve ( ...usual stuff here... );{ } is used in lists of functions, equations or variables where order of listing is unimportant, as in
solve( {x + y = 1, 2*x + 7*y =0}, {x,y} );
plot( {x^2, 2-x^2}, x=-1..1 );
[ ] is used in ordered lists as in vector 
or
, or in 
when plotting
the parametric curve 
. It is also used to refer
to one of the solutions, of a system of equations, obtained by using the
solve command. See subsection 1.11