( r − − r 0 ) ⋅ ⋅ a = ( v − − v 0 ) ⋅ ⋅ v + v 0 2 , where ⋅ ⋅ denotes the dot product, which is appropriate as the products are scalars rather than vectors. 2 ( r − − r 0 ) ⋅ ⋅ a = | v | 2 − − | v 0 | 2 .