/sci/ - Science & Math

So I'm doing some vector stuff as you can see, and I'm trying to find the angle between two vertices. I worked out the dot product first, then I worked out the magnitude of the two vectors and did dot product / magnitude * magnitude. I ended up getting 0.10 for A in this problem set.

My problem is, the answer sheet I'm looking at has "≈1.4716 radians" as the answer.

Can anyone see where I went wrong? I literally can't figure it out, I feel like they've made an error on the result sheet.