LESSON NINTH.

What do we call the angles a o c, c o b? (Diagram [9].)

Are they equal to each other?

Then they are called right angles.

A right angle is one of two adjacent angles that are equal to each other.

Are the adjacent angles c o b, b o d equal to each other?

Then what are they called?

Read the right angles below the line a b. On the left of c d.

Read three right angles whose vertices are at p.

Diagram 9.

Is the angle m p q greater or less than the right angle m p r?

Then it is called an acute angle.

An acute angle is one which is less than a right angle.

Read four acute angles whose vertices are at p.

Acute means sharp.

Why is r p s an acute angle?

What is an acute angle?

Is the angle m p s greater or less than the right angle m p r?

Then it is called an obtuse angle.

An obtuse angle is one which is greater than a right angle.

What other obtuse angle has its vertex at p?

Obtuse means blunt.

Read three obtuse angles whose vertices are at x.

Acute and obtuse angles are also called oblique angles.