Important Points of:

**Collinear Points**: Three points A, B, C are said to be collinear if they lie on the same straight line.**Test for Collinearity of three points**: In order to show that three given points A, B, C are collinear, we find distance AB, BC and AC. If the sum of any two of these distances is equal to the third distance then the given points are collinear.**Centroid of a triangle**: The point of intersection of the medians of a triangle is called its centroid.**Coordinate of Centroid**:(x1+x2+x3)/3, (y1+y2+y3)/3.**Properties of various types of Quadrilaterals**:

- Rectangle: if its opposite sides are equal and the diagonals are equal.
- Square: if all its sides are equal and the diagonals are equal.
- Parallelogram but not a rectangle: if its opposite sides are equal and the diagonal are not equal.
- Rhombus bur not a Square: if all sides are equal and diagonals are not equal.

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