Quadrilaterals
Class 9 · Mathematics
3 ideas in Class 9 Mathematics, explained in plain words, with games and quizzes to practise.
Quadrilaterals and Convexity
Part of: Quadrilaterals and Convexity
A quadrilateral is a planar, non-self-intersecting figure whose sides form a closed boundary. A convex quadrilateral has every interior angle smaller than a straight angle.
Why it matters. Careful definitions help distinguish familiar shapes from crossed, open or dented figures.
Try it in two minutes
- Draw a closed four-sided figure.
- Check that its edges do not cross.
- Look for an inward dent and compare its angles.
Try at home. Find quadrilateral outlines in tiles, windows or books and check whether they are convex.
Parallelogram Properties and Tests
Part of: Parallelogram Properties and Tests
A parallelogram has two pairs of parallel opposite sides. Its opposite sides and opposite angles are equal, its adjacent angles are supplementary, and its diagonals bisect each other.
Why it matters. These properties and their converses provide several ways to identify a parallelogram.
Try it in two minutes
- Draw two crossing diagonals.
- Mark whether each diagonal is split into equal halves.
- Check if opposite sides or angles match.
Try at home. Look for parallelogram properties in hinged frames or linkages.
Midpoint Theorems and Tiling
Part of: Midpoint Theorems and Tiling
A segment joining the midpoints of two triangle sides is parallel to the third side and half as long. The three medians meet at the centroid, which divides each median in a 2 to 1 ratio.
Why it matters. These results connect triangles and parallelograms and help explain how quadrilaterals can tile a plane.
Try it in two minutes
- Mark the midpoints of two sides of a triangle.
- Join them and compare with the third side.
- Locate where the three medians meet.
Try at home. Fold a triangular paper shape to find side midpoints and draw the midpoint segment.
What your child will practise
- Midpoint Theorems and Tiling: Desert Puzzle (Clue Puzzle)
- Midpoint Theorems and Tiling: Ocean Quick Fire (Quick Fire)
- Parallelogram Properties and Tests: Jungle Quick Fire (Quick Fire)
- Parallelogram Properties and Tests: Number Sort (Sort It Out)
- Quadrilaterals and Convexity: Mission Control Quest (Collect the Answer)
- Quiz: Midpoint Theorems and Tiling (8 questions)
- Quiz: Parallelogram Properties and Tests (8 questions)
- Quiz: Quadrilaterals and Convexity (8 questions)