Four-vectors have the same linearity properties as Euclidean vectors in three dimensions. They can be added in the usual entrywise way: A + B = ( A 0 , A 1 , A 2 , A 3 ) + ( B 0 , B 1 , B 2 , B 3 ) = ( A 0 + B 0 , A 1 + B 1 , A 2 + B 2 , A 3 + B 3 ) and similarly scalar multiplication by a scalar λ is defined entrywise by: λ λ A = λ λ ( A 0 , A 1 , A 2 , A 3 ) = ( λ λ A 0 , λ λ A 1 , λ λ A 2 , λ λ A 3 )