Find the angle between `vecA = hati +2hatj - hatk` and `vecB = - hatj + hatj - 2hatk` .

Explanation

We are given: `vecA = hati + 2hatj - hatk` and `vecB = -hati + hatj - 2hatk`
We are to calculate the value of `theta`
We know that,
`vecA. vecB = (hati + 2hatj - hatk) .(-hati + hatj - 2hatk) = -1 + 2 + 2 = 3`
also = `|vecA| = sqrt(1 + 4 + 1) = sqrt(6) and |vecB| = sqrt(1 + 1 + 4) = sqrt(6)`
Using relation: `vecA. vecB = |vecA||vecB|cos theta`
We have, `cos theta = (vecA. vecB)/(|vecA||vecB|) = 3/(sqrt(6).sqrt(6)) = 1/2 "or " theta = 60^@`