The points A(1,2,3), B(4,−1,2), C(6,2,6) and D(3,5,7) are the vertices of a quadrilateral ABCD.
Answer the following questions.
a. (i) Show that ABCD is a parallelogram.
b. (ii) Obtain the vectors representing the diagonals AC and BD.
c. (iii) Find, correct to the nearest degree, the angle between the diagonals AC and BD.