AC and BD are the diagonals of a quadrilateral ABCD, prove that: →AB+→DC=→AC+→DB.
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Solution
Let ABCD be a rectangle, AC and BD its diagonals. In ΔABC, →AB+→BC=→AC →AB=→AC−→BC ...........(i) In ΔBCD by vector law of addition →DC=→DB+→BC ......(ii) by adding (i) and (ii), we get →AB+→DC=→AC−→BC+→DB+→BC →AB+→DC=→AC+→DB