Rather than me explain:
Google finding the angle between 2 3d vectors and go to the uwv teaching tip pdf at the top. It can help you with all your vector questions
If D=7i-3j+2k and E=4i+5j-3k. Deduce angle between D and E
3 answers
D=7i-3j+3k,E=6i+2j-2k
82.83