The same way , in a dimension 3 , the dot product of vectors ( a , b , c ) and ( d , e , f ) is ad + be + cf . For example , the dot product of two three-dimensional vectors ( 1 , 3 , â ' 5 ) and ( 4 , â ' 2 , â ' 1 ) is Similarly , in a dimension 3 , the dot product of vectors ( a , b , c ) and ( d , e , f ) is ad + be + cf .