Hamilton's Math To Build On - copyright 1993


About Math To Build On || Contents || On to Crossing & Parallel Lines || Glossary

* Angles

angles 1-4

    (4) The vertex is the point where the two straight lines come together to form the angle.

* Angle Names

angles 5-12

    (9) A straight angle is an angle of 180° .

    (10) A central angle is an angle of which the vertex is located in the center of a circle.

    (11) Adjacent angles are angles that have the same vertex and one side in common.
      (Adjacent means next to or near).

    (12) Opposite angles are formed by two straight lines crossing and are always equal.
Seeing is Believing: Angle Construction Practice

The compass symbol lets you know there is related information in the section Seeing is Believing -- a very basic mini-drawing section, which is provided just in case you've forgotten, or never learned, some basic drawing rules.

* 90° angles

90 degree angles

The angle most often used in the trades is the 90° angle.
It may help to understand why this is so.

When two straight lines cross, four angles are created.
Those four angles always add up to 360° .

The major lines of the compass are two straight
lines which cross each other at 90° angles.
Most plants and factories are said to be built along
the major lines of the compass.

When lines cross, the only time all four of the angles
created are equal to each other is when each angle is
a 90° angle. A 90° angle is called a right angle.

Seeing is Believing: Fractions of the Ruler

Plumb bob line

On to Crossing & Parallel Lines

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Johnny & Margaret Hamilton
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7 September 1995
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