No space between cos and (
You are inside a list building operation. Spaces can indicate that an entry has ended and a new one is about to begin. MATLAB does not determine a new entry to start if the previous entry ends in one of the binary operators
3+ 5 %all one expression
3 + 5 %all one expression
3 +5 %two expressions, 3 and +5
cos is not a binary operation, so
3 + cos (x)
is two entries, 3+cos and (x). In turn 3+cos is 3+cos() which is the function invoked with no arguments.
