1A circle is built from two lengths: radius and diameter
The radius is the distance from the circle's center to its edge, and the diameter is the distance straight across, connecting two opposite ends. The diameter is always exactly twice the radius.
Diameter = radius × 2
If the radius is 5 cm, the diameter is always 10 cm.
2Triangles are sorted by side length or angle size
Equilateral triangleall three sides are the same length
Isosceles triangletwo sides are the same length
Right triangleone angle is exactly 90°
The same triangle can go by more than one name depending on which rule you look at. For example, a triangle can be both isosceles and a right triangle at the same time.
3Quadrilaterals are also sorted by how many sides are parallel
Squareall four sides and angles are equal
Rectangleall four angles are right angles
Parallelogramboth pairs of opposite sides are parallel
Rhombusall four sides are the same length
Trapezoidonly one pair of sides is parallel
Even if a shape looks crooked, its name stays the same.
Draw a square tilted at an angle, and it's still a square — as long as the rule (all four sides and angles equal) still holds.
Draw a square tilted at an angle, and it's still a square — as long as the rule (all four sides and angles equal) still holds.
A square is also a rectangle, a parallelogram, and a trapezoid, all at once
4Try playing like this
- Look at each shape and find the rule. Check whether the sides are equal, whether any angle is a right angle, and how many pairs of sides are parallel.
- Try the name-that-shape quiz. Practice recalling the rule just from a shape's appearance and naming it correctly.
- Find the overlapping names. A square is both a rectangle and a rhombus at the same time. Check the rules one by one to see why.