Question

Find the angle between the vectors with direction ratio prop to $1,-2,1$ and $4,3,2$.

Answer 1

angle between these two vectors will be $\cos \theta =\frac{1\left(4\right)-2\left(3\right)+1\left(2\right)}{\sqrt{1^2+(-2{)}^2+1^2}\times \sqrt{4^2+3^2+2^2}}=0$

so angle will be $\frac{\pi }{2}$