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Difficulty: 2/102022 NMTC 2022 (QII-60)

Four non-parallel lines in plan intersect at most at

Guide / Hint

Hint 1: The maximum number of intersections occurs when every pair of lines intersects at a unique point.

Hint 2: Use the combinations formula: for lines.

Hint 3: Compute .

Solution

Step 1 (Maximum Intersections Property): The maximum number of intersection points for non-parallel lines occurs when every pair of lines intersects at a unique point.

Step 2 (Apply Combination): The number of ways to choose a pair of lines out of is:

Step 3 (Substitute n = 4):

Step 4 (Conclusion): Four non-parallel lines intersect at most at 6 points.

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    2022 NMTC 2022 QII-60 - Olympiad Math Olympiad Question | Leminno