Question:
The direction ratios of two lines are $3,2,-6$ and $1,2,2$, respectively. The acute angle between these lines is
A. $\cos ^{-1}\left(\frac{5}{18}\right)$
B. $\cos ^{-1}\left(\frac{3}{20}\right)$
C. $\cos ^{-1}\left(\frac{5}{21}\right)$
D. $\cos ^{-1}\left(\frac{8}{21}\right)$
Solution:
