Week 23 · Equivalent fractions and quadrilaterals · 3 lessons
3
Spotting quadrilaterals
Discover Mathematics P3: Term 2, Lessons 91–100
GoalName quadrilaterals and spot them among other shapes by counting sides and checking sides and corners.
New words
quadrilateral · a closed shape with 4 straight sides and 4 cornersopposite sides · sides that face each other across a shaperight angle · a square cornerparallel · always the same distance apart and never meeting
Explanation
A quadrilateral is a closed shape with 4 straight sides and 4 corners. There are many kinds. A square has 4 equal sides and 4 right angles. A rectangle has 4 right angles and equal opposite sides. A rhombus has 4 equal sides, but its corners do not have to be right angles. A parallelogram has two pairs of parallel sides, so its opposite sides are parallel and equal. A trapezium has one pair of parallel sides. Some quadrilaterals have no special name. To spot a quadrilateral, count the sides: a shape with 3 sides is a triangle and a shape with 5 sides is a pentagon. A circle has no straight sides, so it is not a polygon at all.
Worked examples
This parallelogram has two pairs of parallel sides, shown by the one-arrow and two-arrow marks. Its top and bottom sides are both 6 cm long.
Which shapes are quadrilaterals? Count the sides. A is a rectangle with 4 sides, B is a triangle with 3, C is a trapezium with 4 and D is a pentagon with 5. So A and C are quadrilaterals.
This shape has 4 straight sides and 4 corners, but no equal sides and no parallel sides. It has no special name, but it is still a quadrilateral.
Class activity
Shape hunt. Walk around your home or school with an adult and find five things with a flat side shaped like a quadrilateral, such as a tile, a window, a door or a table top. Draw each one, count its sides and write its name: square, rectangle, rhombus, parallelogram or trapezium.
Practice
1
How many sides and how many corners does a quadrilateral have?
A quadrilateral has 4 sides and 4 corners.
2
Which of the shapes are quadrilaterals?
B and D. B is a square and D is a trapezium. A has 3 sides and C has 6 sides.
3
Which quadrilateral has all four sides equal and all four corners square?
It is the square: no other quadrilateral has all sides equal and all corners square.
4
All four sides of this shape are 5 cm and its corners are not square corners. What is it?
It is a rhombus: 4 equal sides and no right angles.
5
Youssef says a rectangle is a quadrilateral but a trapezium is not. Is he right?
No. A trapezium has 4 straight sides, so it is a quadrilateral too.
