Math-Scene - Degrees and angles lesson 2

Degrees and angles lesson 2.

Corresponding angles

Angles are said to be corresponding if the line n is the left ( or right) arm of both angles with the lines m and l forming the other arms.

Example: <a and <e are corresponding angles, the line n is the right arm of both angles.

Example: <g and <b are corresponding angles, the line n is theleft arm of both angles.

Rules for corresponding angles

If two corresponding angles are equal then the lines l and m are parallel. Conversely if the lines l and m are parallel then the corresponding angles are equal.

Angle at the centre of a circle

This is the angle with its vertex at thecentre of the circle and the radii OA and OB forming the arms of the angle

The angle at the centre and the arc of the circle it spans are equal in degrees.

The angle <AOB is 120 ° and the arc AB is also120°.

Angle on the circumference

This is an angle that has its vertex on the circumference of a circle and chords of the circle, AB and AC form the arms of the angle.

An angle on the circumference of a circle is half the size of the arc, BC ,that it stands on.

Interior angles of a circle

The size in degrees of angle O is the average of the arcs AB andCD.

In this example angle < O is

<O = 40 °.

Exterior angles of a circle

Tha angle <O is half the difference between the arcs AD and BC.

<O = 30 °.

Practice these rules then take test 2.

ps. remember to fill in your check list as you go along.