Binary Arithmetic Operators: $+,-,->*(),$ and $*()$ will be

overloaded as friend functions. The $$ operator denotes the cross product $()$ operator. The $+$ operator has been implemented for you. The

operators addition $+,$ subtraction $-,$ cross product $*(),$ and the scalar

product return vectors. Observe that the $*$ operator is also overloaded

as a scalar product, kv $=$ k $<$ v$1,$ v$2,$ v$3>=<$ kv$1,$ kv$2,$ kv$3>,$ where

k is a number and v is a vector. The dot product, however, $->()$

operator returns a number $($scalar$)$