Question

If `A= <7 ,-5 ,1 >` and `B= <8 ,6 ,7 >`, what is `A*B -||A|| ||B||`?

Answer 1

`-72.712`

Explanation:

`A*B=(7,-5,1)*(8,6,7)`

`=(7xx8)+(-5xx6)+(1xx7)`

`=56-30+7`

`=33`.

`||A||=sqrt(7^2+5^2+1^2)=sqrt75`.

`||B||=sqrt(8^2+6^2+7^2)=sqrt149`.

`therefore A*B-||A||||B||=33-(sqrt75)(sqrt149)`

`=-72.712`.