Question

If `A= <2 ,-3 ,-4 >` and `B= <-1, 3, 7 >`, what is `A*B -||A|| ||B||`?

Answer 1

The answer is `=80.4`

Explanation:

We calculate the dot product

`vecA.vecB=<2,-3,-4>.<-1,3,7>`

`=-2-9-28=-39`

The modulus of `vecA=||<2,-3,-4>||`

`sqrt(4+9+16)=sqrt29`

The modulus of `vecB=||<-1,3,7>||`

`=sqrt(1+9+49)=sqrt59`

Therefore,

`vecA.vecB-||vecA||*||vecB||`

`=-39-sqrt29*sqrt59`

`=-80.4`