Lesson · Grade 4 · Mathematics
Regular and Irregular Polygons
- Grade 4
- Mathematics
- 1 min 27 s
- British Columbia
- BC4-MA-23
A polygon is a closed shape with straight sides, and it is regular only when all its sides and all its angles are equal. A square, a rectangle and a rhombus each get the same two checks: the square (four 3 cm sides, four 90° angles) is regular, the rectangle (5, 3, 5 and 3 cm) and the rhombus (angles of 60°, 120°, 60° and 120°) are irregular, and the video ends with regular polygons that have 3, 4, 5 and 6 sides.
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In one sentence
The question this lesson answers
How can we tell if a polygon is regular or irregular?
A polygon is a closed shape with straight sides.
Transcript
What the lesson says
How can we tell if a polygon is regular or irregular?
A polygon is a closed shape with straight sides.
A regular polygon has all sides equal and all angles equal.
Every side of the square is 3 centimetres, so the sides are equal.
Every angle is a right angle, 90 degrees, so the angles are equal.
The sides and the angles are all equal, so the square is regular.
This rectangle has sides of 5, 3, 5 and 3 centimetres, not all equal.
Every angle is 90 degrees, so the angles are equal.
The sides are not all equal, so this rectangle is irregular.
Every side of this rhombus is 3 centimetres, so the sides are equal.
But its angles are 60, 120, 60 and 120 degrees, not all equal.
The angles are not all equal, so this rhombus is irregular.
Of these three shapes, only the square is regular.
Regular polygons can have 3, 4, 5, 6 or even more sides.
A polygon is regular only when all its sides and all its angles are equal.
Curriculum
Where this fits
- British Columbia, Grade 4
Mathematics, Geometry and measurement: regular and irregular polygonsBC4-MA-23
Previous: 3:15 p.m. or 15:15? Morning, afternoon and the 24-hour clockNext: Perimeter: the distance around a shape
The outcomes and strands follow the British Columbia curriculum.
Keep going
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Grade 5 · 1 min 21 s
1 min 5 sArea of a Circle from the Radius or the Diameter
Grade 7 · 1 min 5 s
1 min 14 sArea of a Parallelogram: Cut and Slide into a Rectangle
Grade 6 · 1 min 14 s
1 min 18 sArea of a Rectangle: Count the Squares, Then Multiply
Grade 5 · 1 min 18 s
1 min 16 sArea of a Trapezoid: Two Copies Make a Parallelogram
Grade 6 · 1 min 16 s
1 min 19 sArea of a Triangle: Half of a Parallelogram
Grade 6 · 1 min 19 s
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