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Consider a chessboard of size 8 units × 8 units (i.e. each small square on the board has a side length of 1 unit). Let S be the set of all the 81 vertices of all the squares on the board. What is number of line segments whose vertices are in S1 and whose length is a positive integer ? (The segments need not be parallel to the sides of the board.) |
Answer» Number of line segment parallel to co-ordinate axis of 1 unit length equals to 8 × 9 × 2. Number of line segment parallel to co-ordinate axis of 2 unit length equals to 7 × 9 × 2. Number of line segment parallel to co-ordinate axis of 3 unit length equals to 6 × 9 × 2. and soon….. Number of line segment parallel to co-ordinate axis of 8 unit length equals to 1 × 9 × 2. Number of line segment not parallel to co-ordinate axis of 5 unit length equals to 5 × 8 × 2 × 2. Number of line segment not parallel to co-ordinate axis of 10 unit length equals to 7 × 3 × 2 × 2. Total line segment equals to 780. |
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