Example

Example of Testing for Collinear Points Using Determinants

To determine whether three points are collinear, substitute their coordinates into a 3×33 \times 3 determinant with a column of ones. For example, to check the points (5,−5)(5, -5), (4,−3)(4, -3), and (3,−1)(3, -1), evaluate: ∣5−514−313−11∣\begin{vmatrix} 5 & -5 & 1 4 & -3 & 1 3 & -1 & 1 \end{vmatrix}. Expanding by minors along the third column yields 1(4(−1)−3(−3))−1(5(−1)−3(−5))+1(5(−3)−4(−5))=1(−4+9)−1(−5+15)+1(−15+20)=5−10+5=01(4(-1) - 3(-3)) - 1(5(-1) - 3(-5)) + 1(5(-3) - 4(-5)) = 1(-4 + 9) - 1(-5 + 15) + 1(-15 + 20) = 5 - 10 + 5 = 0. Since the determinant equals 00, the points are collinear.

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Updated 2026-06-25

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