1. The problem statement, all variables and given/known data Find the smallest interior angle of the triangle ABC whose vertices are given. A = (3,1,-2), B = (3,0,-1), C = (5,2,-1) 2. Relevant equations I think the equation arccos( U dot V / (lengthU)(lengthV) 3. The attempt at a solution What i did is tried the formula for all combinatations: AB, BC, AC to get all the angles, and which ever was the smallest I choose. Unfortunately I do not get the correct answer.