Given the player position (5,10,6);
Given the triangle P1(0,-10,0) P2(0,0,50) P3 (50,5,0);

How do I fire a ray from the player which is above the triangle, down into the triangle and determine if there is going to be an intersection?

I believe rays go on forever...but this ray needs to terminate after it has travelled the length of the players new pos minus his old pos...