1. The problem statement, all variables and given/known data We consider two points, B and I and a line 'a'. B(0,-4,-7) I(-2,-2,-5) and a: x = y+1 = (z-2)/2 Determine the summits of A and C of triangle ABC knowing that: -Summit A belongs to the line 'a' -I is the foot of the height from A (perpendicular to BC) -The angle of A is equal to arccos(1/3) 2. Relevant equations dot product 3. The attempt at a solution I feel as if I'm really close, but keep getting the wrong answer. My process is as follows: The dot product of BI and AI is equal to zero. Knowing this, I can obtain an equation of the line AI and determine where it intersects with line 'a'. This is as far as I've gotten in my attempt to find A. Thanks a lot for any help you can provide!!