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Triangles or polygons from points on the sides of a figure

This type of question, asked 5 times: 2021 Paper 6, 2021 Paper 8, 4 Apr 2024, 3 Apr 2025, 22 Jan 2026 S1. All 5 questions below, oldest first.

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  1. Question 1

    2021 Paper 6

    71
    Consider a rectangle ABCDABCD having 5, 7, 6, 9 points in the interior of the line segments ABAB, CD,BC,DACD,BC,DA respectively. Let α\alpha be the number of triangles having these points from different sides as vertices and β\beta be the number of quadrilaterals having these points from different sides as vertices. Then (β−α)(\beta-\alpha) is equal to:

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  2. Question 2

    2021 Paper 8

    71
    If the sides AB,BCAB,BC and CACA of a triangle ABCABC have 3,5 and 6 interior points respectively, then the total number of triangles that can be constructed using these points as vertices, is equal to:

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  3. Question 3

    4 Apr 2024

    68
    There are 5 points P1,P2,P3,P4,P5P_{1},P_{2},P_{3},P_{4},P_{5} on the side ABAB, excluding AA and BB, of a triangle ABCABC. Similarly, there are 6 points P6,P7,…,P11P_{6},P_{7},\ldots,P_{11} on the side BCBC and 7 points P12,P13,…,P18P_{12},P_{13},\ldots,P_{18} on the side CACA of the triangle. The number of triangles, that can be formed using the points P1,P2,…,P18P_{1},P_{2},\ldots,P_{18} as vertices, is:

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  4. Question 4

    3 Apr 2025

    133
    Line L1L_{1} of slope 2 and line L2L_{2} of slope 12\frac{1}{2} intersect at the origin O . In the first quadrant, P1,P2,….P12P_{1},P_{2},\ldots.P_{12} are 12 points on line L1L_{1} and Q1,Q2,…..Q9Q_{1},Q_{2},\ldots..Q_{9} are 9 points on line L2L_{2}. Then the total number of triangles, that can be formed having vertices at three of the 22 points O,P1,P2,…P12O,P_{1},P_{2},\ldots P_{12}, Q1,Q2,….Q9Q_{1},Q_{2},\ldots.Q_{9}, is:

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  5. Question 5

    22 Jan 2026 S1

    75
    Let ABC be a triangle. Consider four points p1,p2p_{1},p_{2}, p3,p4p_{3},p_{4} on the side AB , five points p5,p6,p7,p8,p9p_{5},p_{6},p_{7},p_{8},p_{9} on the side BC and four points p10,p11,p12,p13p_{10},p_{11},p_{12},p_{13} on the side AC . None of these points is a vertex of the triangle ABC . Then the total number of pentagons, that can be formed by taking all the vertices from the points p1,p2,….p13p_{1},p_{2},\ldots.p_{13}, is ____\_\_\_\_ .