I wasn't sure if that was necessary info or not... looks like I was wrong :)
If U and V are subspaces of vector space W, and each w in W can be written uniquely as a sum u+v where u is in U and v is in V then W is a direct sum of U and V.
Let U and V be subspaces of a vector space W. If W=U \oplus V, show U \bigcap V={0}.
I'm a bit lost on this one... as I thought this was essentially the definition of direct sum. I'm unsure where to start. Any help would be great!