Question

Find the angle between two lines whose direction ratios are $(2,3,6)$ and $(1,2,2)$.

Answer 1

Angle will be $\cos \theta =\frac{2\left(1\right)+3\left(2\right)+6\left(2\right)}{\sqrt{2^2+3^2+6^2}\times \sqrt{1^2+2^2+2^2}}=\frac{20}{21}$

$\theta ={\cos }^{-1}\left(\frac{20}{21}\right)$