Scalar Product and the Ratio Theorem  
Summary

vectors can be multiplied in two ways. one such way is called the vector product or cross product. the one covered in this unit is called the scalar product or dot product. the scalar product can be used to find the angle between two vectors. the scalar product can be used for two or three dimensional vectors. the scalar product of two perpendicular vectors is zero. perpendicular vectors are said to be orthogonal. the ratio theorem uses vectors to find the coordinates of a point dividing a line in a certain ratio, either externally or internally. 
Key Skills 

Vocabulary 
scalar product, orthogonal, ratio theorem, vector product, cross product, dot product. 