Question

What is the angle between `<<-7,5,-9>>` and `<<-1,-2,1>>`?

Answer 1

113.17 deg, nearly

Explanation:

The angle between the vectors (x, y, z) and (u, v, w) is
arc cos { (xu +yv + zw) / (`sqrt`(x.x + y.y + z.z).`sqrt`(u.u + v.v + w.w)}.
Here, the angle is arc cos (`-`12 / `sqrt`930)