Question

What is the angle between `<-9 , 2 , -4 >` and `< 5 , 2 , 0 >`?

Answer 1

139.25 deg.

Explanation:

Let the vectors be called AC and AB.
Then the vector BC = AB - AC = <14, 0, 4>.
The sides a, b and c of the`triangle`ABC are 2`sqrt`53, `sqrt`101 and `sqrt`29.
The angle at A is arccos (( b.b + c.c - a.a ) / (2bc)).= arccos ( - 0..7576) =139.25 deg.