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

10. Go through the same demonstrations again, calling the angles by their letters instead of by their colors.

By means of Fig. B,—

11. Prove the interior opposite angles a g h, g h c, equal to two right angles, using the angle g h d.

12. Prove the same, using the angle c h f.

13. Prove the same, using the angle a g e.

14. Prove the interior opposite angles b g h, g h d, equal to two right angles, using the angle a g h.

15. Prove the same, using the angle e g b.

16. Prove the same, using the angle f h d.

Compare the angles Yellow, Green, each with its exterior opposite angle, and see if you can prove that the exterior opposite angles e g b, f h d, are also equal to two right angles.