1. The problem statement, all variables and given/known data Ok so i ran into trouble in the momentum section because i do not understand dot products as well as i thought. I tried going back and revising my notes but nothing new comes to mind. Your help is highly appreciated. ok so let me just state that m1=m2 the problem consists of 2 billiard balls, one is at rest and the other strikes it and sends it towards the corner pocket, they both share the same mass. the purpose is to find theta, but that is not what i'm trying to find out here. We write the kinetic formula which gets reduced to v1i^2 = v1f^2 + v2f^2 then the momentum formula also gets reduced, this time it gets reduced to : v1i = v1f + v2f. what i can't figure out, is that the example tells me to to square both sides (of the previous formula) and find the dot product. then i get v1i^2 = (v1f + v2f)(v1f+v2f)... which gets expanded.. and so on [the formula makes sense from a logical point of view] The point is, how is the equation above, the DOT PRODUCT. I don't get that. i thought the dot product formula is AB = ABCOS(THETA) any explanations?