Find the angle between the lines `vecr = (hati+hatj)+lambda(3hati+2hatj+6hatk)` and `vecr = (hati-hatk) + mu(hati+2hatj+2hatk)`

Explanation

Here `vecm = 3hati+2hatj+6hatk` and `vecn=hati+2hatj+2hatk`
Let ` theta` be the angle between two lines .
`:. cos theta = (vecm.vecn)/(|vecm||vecn|) = ((3hati+2hatj+6hatk).(hati+2hatj+2hatk))/(|3hati+2hatj+6hatk|| hati+2hatj+2hatk|)`
`= (3+4+12)/(sqrt(9+4+36)sqrt(1+4+4)) = (19)/(7xx3) = (19)/(21)`
`theta = cos^(-1) (19/21)`