### Lesson 3: Angles, Triangles, and Rectangles (Form)

The instructor tells children:

- Form tells about the shape of objects.
- The simplest forms are triangles, rectangles, circles, ellipses, and ovals.
- These forms in mathematics are called geometrical forms, and in drawing, measures of form.
- These measures of form are common in animals and birds.
- When it comes to the triangle, "tri" means three and "triangle" means three angles.
- Thus, a triangle is a figure with three angles.
- To call out the general shape of each animal in the top picture.

The instructor:

- Asks children to study the image labeled "Angles, Triangles, and Rectangles."
- Tells children that right means straight, acute means sharp, and obtuse means dull.
- Uses their forefinger to make right angles, acute angles, and obtuse angles and asks children to name each one as they are made.
- Asks children to find these angles in their surroundings.

Children complete the following drill work:

- Draw a right angle.
- Draw an acute angle.
- Draw an obtuse angle.
- Draw a right triangle.
- Draw an acute triangle.
- Draw an obtuse triangle.
- Draw a square rectangle.
- Draw a vertical rectangle.
- Draw a horizontal rectangle.
- Draw a shed form.
- Draw a house form.