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

Then will any two adjacent angles, as Green, Red, be equal to two right angles?

For, from the point c, draw the straight line c d so as to make the angles a c d, d c b, right angles.

The adjacent angles Green, Red, are equal to all the angular space on the line a b.

The right angles a c d, d c b, are also equal to all the angular space on the line a b.

Therefore the adjacent angles Green, Red, are equal to two right angles.

TEST QUESTIONS.

To what same thing did you find two things equal?

What did you first see equal to it?

What did you next see equal to it?

Then what new thing did you find true?