Question

What is the angle between `<-8,-5,2 >` and `<9,1,-3>`?

Answer 1

Angle between vectors is approximately `**154.5°**`.

Explanation:

I've added image which might help

Also this link will help
http://www.wikihow.com/Find-the-Angle-Between-Two-Vectors

Actually the inverse cosine is approximately `154.5°` instead of `90°`. We cannot tell what happened to make the mistake, but it looks as if the answerer forgot the decimal point in 91.99 when entering the inverse trigonometric function into the calculator.