LESSON FIFTEENTH.

Are the angles e m b, b m n, on the same side of the intersecting line e f?

Are they adjacent?

Are e m b, m n d, on the same side of the intersecting line e f?

Are they adjacent?

Then they are called opposite angles.

Opposite angles lie on the same side of the intersecting line, but are not adjacent.

Are the angles e m b, f n d, on the same side of the intersecting line?

Are they adjacent?

Then are they opposite?

Are they interior or exterior angles?

Then they are “opposite exterior angles.”

Why are they exterior?

Why are they opposite?

Are the angles b m n, m n d, opposite angles?

Are they interior or exterior angles?

Then they are “opposite interior angles.”

Why are they opposite? Why interior?

Read the opposite exterior angles on the left of the line e f.

Read the opposite interior angles on the same side.

Are the opposite angles e m a, m n c, both exterior or interior?

Then they are opposite exterior and interior angles.

Read two pairs of opposite exterior and interior angles on the right of e f. On the left.

Do the angles b m n, m n c, lie on the same side of the intersecting line e f?

Are they adjacent to each other?

Are they vertical angles?

Then they are alternate angles.

Alternate angles lie on different sides of the intersecting line, and are neither adjacent nor vertical.

Are the alternate angles b m n, m n c, exterior or interior?

Then they are called “interior alternate angles.”

Read another pair of interior alternate angles between a b and c d.

Are the angles e m b, c n f, alternate angles? Why?

Are they exterior or interior?

Then what may they be called?

Read another pair of exterior alternate angles.

Why are e m a, d n f, alternate angles? Why exterior alternate?