Triangles and quadrilaterals
Sort triangles by their sides and angles, meet the quadrilateral family, and draw the diagonals of a rhombus.
- UK: Year 4
- France: grade 3
- Germany: grade 1
- Iran: grade 4
- Afghanistan: grade 5
- Syria: grade 4
- Palestine: grade 3
- Ukraine: grade 3
- Russia: grade 5
Guide
This studio is for Years 4 and 5. Like many textbooks, it works on dotty paper.
Triangles have two kinds of name. By sides: equilateral triangle (three equal sides), isosceles triangle (at least two equal sides) and scalene triangle. By angles: acute-angled triangle, right-angled triangle and obtuse-angled triangle. A triangle can be right-angled and isosceles at the same time.
On dotty paper, a slanted side that goes "2 across, 1 up" is the same length as one that goes "1 across, 2 up". That helps to spot equal sides on tilted triangles.
Quadrilaterals form a family: a square is a rectangle (four right angles) and also a rhombus (four equal sides). Rectangles and rhombuses are both parallelograms. In this studio a trapezium has exactly one pair of parallel sides, as in Iran's books. The diagonals of a rhombus cross at right angles and cut each other in half.