Find the area of the parallelogram whose adjacent sides are determined by the vectors

If either then Is the converse true? Justify your answer with an example.

Find the area of the triangle with vertices A(1, 1, 2), B(2, 3, 5) and C(1, 5, 5).

Let the vectors be such that then is a unit vector, if the angle between is

Area of a rectangle having vertices A, B, C and D with position vectors respectively is