# What is the angle between <9,-8,1 >  and < 4,-7,1 >?

$< 9 , - 8 , 1 > \cdot < 4 , - 7 , 1 \ge | < 9 , - 8 , 1 > | | < 4 , - 7 , 1 > \cos \theta$
$\left(36 + 56 + 1\right) = \left(\sqrt{{9}^{2} + {8}^{2} + {1}^{2}}\right) \left(\sqrt{{4}^{2} + {7}^{2} + {1}^{2}}\right) \cos \theta$
$93 = 98.1631 \cos \theta$
$\cos \theta = 0.9474$
$\theta = {\cos}^{-} 1 0.9474$
$\theta = 0.325784303 r a d$