Find the angle between two vectors. `A=hati+2hatj-hatk and B=-4hati+hatj-2hatk`.

Explanation

`AB=|A||B|cos theta, cos theta=(A.B)/(|A||B|)`
`A.B=(hati+2hatj-hatk).(-4hati+hatj-2hatk)=-4+2+2=-4+4=-4+4=0`
`cos theta=0, theta =cos^(-1)0, theta=90^(@)`
Hence, the angle between two vectors of A and B is `90^(@)`.