Dot Product
posted by Putnam .
Verify using an example that Vector a • (Vector b • Vector c) = (Vector a • Vector b) • Vector c is not true. Explain your reasoning both numerically and by using the definition of the dot product. I am very confused as to what this means?! Thanks for the assistance.

It wants you to substitute values (can be anything as far as I know) for each vector into that equation, then explain based on what you know of the definition of a dot product its properties.
For example:
<2,3> dot (<1,4> dot <3,3> = (<2,3> dot <1,4>) dot <3,3>
Work that out, and the two sides should be different answers. Then explain why that is...I'm guessing due to that multiplication property or something along those lines... 
Awesome! Thanks, billy!