Angle sum of triangle
Angles of a triangle add up to 180° - proof by rotation and translation.

Tessellation of triangle
All triangles tessellate using rotation and translation.

Tessellation of quadrilateral
All quadrilaterals tessellate using rotation and translation.

Pythagoras' Theorem
A square is made with the two small squares and four triangles and an identical square is made with the largest square and four triangles.

Symmetry
A shape with order of rotational symmetry 4 and no reflective symmetry and a shape with order of rotational symmetry 2 and 2 lines of symmetry.

Gradient of tangent
gradient of the tangent as the limit of the gradient of the secant