Question

Find a dot b given that ...(please see description)? Thanks

Suppose `vec"OA"=a`, `vec"OB"=b`, `|a|=3`, `|b|=sqrt7` and `atimesb= i +2j-3k`
Find `a*b`

Answer 1

`+-7.`

Explanation:

We know that,

`|veca*vecb|^2+|vecaxxvecb|^2=|veca|^2|vecb|^2.`

`:. |veca*vecb|^2+{sqrt(1^1+2^2+(-3)^2)}^=3^2(sqrt7)^2.`

`:. |veca*vecb|^2+14=63.`

`:. |veca*vecb|^2=49.`

`rArr veca*vecb=+-7.`