Coordinate Geometry — Revision Notes
Tamil Nadu Board · Class 10 · Mathematics
Coordinate Geometry revision notes for Tamil Nadu Board Class 10 Mathematics: 4 topics in quick points. Includes Area of Triangle Using Coordinates.
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Key Topics to Revise
1. Area of Triangle Using Coordinates
- Area formula when three vertices are known: Area = ½|{(x₁y₂ + x₂y₃ + x₃y₁) - (x₂y₁ + x₃y₂ + x₁y₃)}|
- Vertices must be taken in counter-clockwise order to avoid negative areas
- Three collinear points always form a triangle with area = 0
2. Collinearity Test Using Slope and Area
- Method 1: Three points are collinear if area of triangle = 0
- Method 2: Three points A(x₁,y₁), B(x₂,y₂), C(x₃,y₃) are collinear if x₁(y₂-y₃) + x₂(y₃-y₁) + x₃(y₁-y₂) = 0
- Method 3: Points are collinear if slope of AB = slope of BC = slope of AC
3. Area of Quadrilateral Using Coordinates
- Quadrilateral area = Area of △1 + Area of △2 (divide using diagonal)
- Standard formula: Area = ½|{(x₁y₂ + x₂y₃ + x₃y₄ + x₄y₁) - (x₂y₁ + x₃y₂ + x₄y₃ + x₁y₄)}|
- Take vertices in counter-clockwise order for consistency
4. Slope of a Line and Its Properties
- Slope m = tan(θ) where θ is angle with positive x-axis (inclination)
- Slope formula: m = (y₂-y₁)/(x₂-x₁) for points (x₁,y₁) and (x₂,y₂)
- Slope = 0 for horizontal lines (parallel to x-axis)
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