1. For which value of a are the following four points contained on the same plane: A = (2,1,3), B = (1,2,1), C = (1,0,0), D = (a, 1, 1). Find the equation of this plane. 2. Find the point of intersection between the line given parameterically by r(t) = 1+t, y(t) = 2-4t, 2(t)=-1-t and the plane x+y+2z = 1. 3. Consider line I given by r(t) = t, y(t) = 1+t, z(t) = -1-t and line II given by r(t) = t-1, y(t) = 3-t, z(t) = 1-t. Do the two lines intersect? If they do, find the point of intersection. If they do not, explain how you can tell.