Question

What is the angle between `<-4 , 0 , -1 >` and `< 8 , 6 , 3 >`?

Answer 1

144.4 deg, nearly.

Explanation:

Let the vectors be called AC and AB.
Then the vector BC = AB - AC = <12, 6, 4>.
The sides a, b and c of the `triangle`ABC are 14, `sqrt`17 and `sqrt`109.
The angle at A is arccos (( b.b + c.c - a.a ) / (2bc).= arccos( -0.8131) =144.4 deg.