I need to plot the band structure of Graphene using Maple, Ive written out the eqn as given in the homework, but when i hit enter it says "error. unable to match delimiters"

i have no idea what that means, here is the eqn i have typed into Maple:

http://imageshack.us/photo/my-images/39/j7ri.jpg/

http://img39.imageshack.us/img39/733/j7ri.jpg

i have been given values for gamma and acc, do i just type them in after, E is a function of k (kx,ky,kz) do i put that in brackets after the E?

E(kx,ky,kz)