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If A(1, 5), B(2, 3) and C(−2, −11) — find whether these three points are collinear.

Class 10Coordinate GeometryGeometry — Coordinates
  • ANo, area is not zero
  • BYes, area is zero
  • CCannot be determined
  • DYes, all are equidistant

Step-by-Step Solution

Area = (22) = 11 ≠ 0. Not collinear.
Answer: A) No, area is not zero

Key idea: Area of a triangle from vertices

Given A₁, ₁), B₂, ₂), C₃, ₃), the area is:

**Area = ₁₂ − ₃) + ₂₃ − ₁) + ₃₁ − ₂)|**

The absolute value sign |·| ensures area is positive regardless of vertex order.

**Use case 1**: Compute area without drawing anything.
**Use case 2**: Test for COLLINEARITY — three points are collinear iff the (signed) area expression equals 0.

**Example**: A(1, 1), B(2, 3), C(4, 5).
Area = ·2 = 1.
Non-zero → not collinear.

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