Hamilton's Math To Build On - copyright 1993

Degrees: Circles, Triangles, Rectangles, Squares

About Math To Build On || Contents || On to Variables & Constants || Back to Degrees || Glossary

* Circles

You already know that a circle has 360° . Circles can be divided into different sectors: a half circle or semi-circle has 180° , a quarter circle has 90° , and an eighth of a circle has 45° .

Circles are covered in more detail elsewhere in the book.


* Triangles

A triangle is a closed figure that has three sides and three angles.

The sum of the three angles of every triangle always equals 180° .

A right triangle always has one angle equal to 90° and two angles whose sum is 90° , making a total of 180° .


* Rectangles

A rectangle is a four sided shape
with four right angles
(90° ).

The sides across from each other are always
the same length and always parallel to
each other.

The four angles add up to a total of 360° .

Another important rule about rectangles is that the diagonals of a rectangle are equal.

Diagonals are lines that run between opposite corners.

A diagonal always divides a rectangle exactly in half and creates two equal right triangles.

Carpenters doing layout work on forms 
measure both diagonals to make sure they
are the same length. This insures that their
layout is a rectangle which has square


* Squares

The square is a special type of rectangle in which all sides
are equal. Since the square is a rectangle, the same rules
that apply to the rectangle also apply to the square.

A diagonal across the square creates two equal
45° right triangles.

Later, you will be working with
45° right triangles.

It will be helpful to remember
that the 45° right triangle is
half of a square.

On to Variables and Constants

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9 September 1995
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