Illuminations: Describing Designs
Illuminations (National Council of Teachers of Mathematics)

Students create designs and describe them to a classmate, using fractional and geometric terms.

Illuminations: The Plus Sign and Triangle
Illuminations (National Council of Teachers of Mathematics)

Using a scheme similar to the one in the Rectangle lesson of this unit, students will further explore the concepts of identity, inverse, and commutative and associative properties.

Illuminations: Discovering the Area Formula for Triangles
Illuminations (National Council of Teachers of Mathematics)

In this lesson, students develop the area formula for a triangle.

NRICH: Pythagoras Perimeters
NRICH (University of Cambridge)

If you know the perimeter of a right angled triangle, what can you say about the area?

NRICH: Terminology
NRICH (University of Cambridge)

Given an equilateral triangle inside an isosceles triangle, can you find a relationship between the angles?

NRICH: Linear Area
NRICH (University of Cambridge)

Find the area of the triangle enclosed by these lines.