Marks' first lessons in geometry / In two parts. Objectively presented, and designed for the use of primary classes in grammar schools, academies, etc.

by Bernhard Marks

LESSON ELEVENTH.

RELATIONS OF LINES.

PERPENDICULAR LINES.

What kind of angles do the lines a b and c d make with each other? (Diagram [11].)

Then they are perpendicular to each other.

What line is perpendicular to x y?

Why is it perpendicular to it?

What line is perpendicular to z 1?

When is a line said to be perpendicular to another?

Can a line standing alone be properly called a perpendicular line?

What two lines are perpendicular to the lines r s?

Is the line g h perpendicular to the line i j? Why?

What other line is perpendicular to the line i j?

Read three lines that are perpendicular to the line a b.

PARALLEL LINES.

Do the lines k l, m n, differ in direction? Then do they form any angle with each other?

They are said to be parallel to each other.

Read four other lines that are parallel with k l.

What line is parallel with 2 10?

Why?

Lines are parallel with each other when they do not differ in direction.

OBLIQUE LINES.

What kind of angles do the lines u t and 8 9 form with each other?

Then they are said to be oblique to each other.

Lines are oblique to each other when they form oblique angles.

See Note [C], Appendix.

Diagram 12.