Maple has many commands to manipulate algebraic expressions. A few of them
are collect, expand, simplify, combine - use the ? to find out
more about them. To extract parts of an expression two useful commands
are op and nops. Briefly, nops(a) gives the number of
operands (i.e. pieces) in expression a, while op(3,a) returns
the third operand (i.e. piece) of the expression a. As an example, we show
how to extract all the terms containing 
in an expression. Try
a := (x^2 + y*sin(3*x))*x*y + 5*(y^2+x^2)*sin(3*x) + y*sin(x)^3 ; b := collect(a, sin(3*x)); collect coeff of powers of sin(3x) nops(b); number of operands/pieces in b c := op(1,b); get first part of b - contains the terms with sin(3x) nops(c); number of pieces in c - want coefficient of sin(3x) op(1,c); gives coeff of sin(3x)
