A tent with no bottom stands in a terrain. The tent has three rods that are gathered in T = (1,1,4). The tent bars stands in the points A = (0,0,0), B = (3,1,1) and C = (- 1,3,2). The tent must be supported by an additional rod which is in a point D and attached to T. The rod is perpendicular to the ground.
a) Find the length of this rod.
b) Find the coordinates of point D.
The Attempt at a Solution
I do not know where to start. I thought about using DT*DC=0, but it didn't lead me anywhere. I'm struggeling with both of the tasks by the way.