# If A = <4 ,2 ,-5 >, B = <-8 ,4 ,9 > and C=A-B, what is the angle between A and C?

Feb 23, 2016

arc cos (19 / sqrt430) = 23.6 deg, nearly.

#### Explanation:

C = <12, $-$2, $-$14>.
The angle between A and C is
arc cos (A.C/(product of the lengths of A and C))