1. The problem statement, all variables and given/known data If A = 1i + 2j + 3k and B = 1i + 2k, and if C = A X B, then the angle between the vector A and the vector C is: 2. Relevant equations AxB = ((a2b3-a3b2)i + (a3b1-a1b3)j + (a1b2-a2b3)k) A·B = ABcosθ = AiBi + AjBj + AkBk 3. The attempt at a solution I got C = 4i + j -2k and A = 1i + 2j + 3k A·C = 4i + 2j - 6k with a magnitude of 7.48 then I used the magnitude of A and C individually to get 3.74 and 4.58 respectively. The I used the equation cos-1(7.48/(3.74 x 4.58)) = θ θ = 64.11 degrees. The actual answer is 90 degrees. What am I doing wrong?