isnt area of a parellelogrm = d1*d2
where d1,d2 are the two diagonals.
No, that is not true in general. I'm sure you're thinking of the rhombus, which is a special type of parallelogram- one with all sides equal; the area of a rhombus is one half of the product of the diagonals (and not the product). But you can see, by looking at a rectangle with length 4 and width 3 (and thus diagonals of 5), that if a parallelogram is not a rhombus, the area will not in general be equal to half the product of the diagonals.
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