Question: the diagonals of a parallelogram are 2i and 2j?
Answer: If the diagonals AC and BD of a parallelogram ABCD are represented by two vectors a and b respectively then the area of the parallelogram is equal to( 1/2) | a ×b | . Here a=2i and b=2j. Hence area = (1/2) | 2i ×2j|=2| i ×j |=2|k|=2 sq. unit.