ABCD – parallelogram, designate vector AC and vector DB through vectors AB and AD.

Since the lengths of the opposite sides of the parallelogram are equal, then AB = DС, AD = BC.

Then the vector | ↑ DС | = | ↑ AB |.

Vector | ↑ AC | = | ↑ AD | + | ↑ DС |.

Vector | ↑ DВ | = | ↑ DA | + | ↑ AB | = – | ↑ AD | + | ↑ AB | = | ↑ AB | – | ↑ AD |.

Answer: Vector | ↑ AC | = | ↑ AD | + | ↑ DС |, vector | ↑ DВ | = | ↑ AB | – | ↑ AD |.



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