Page:An introduction to linear drawing.djvu/25
20. Make an acute angle. (fig. 7.)
Care must be taken to distinguish an angle, from what is called its point or apex. The angle is the opening between two lines that meet, and the point or apex is the point where the lines meet. A pair of dividers forms a number of different angles, by being opened more or less.
It is this opening of the sides which determines the size of the angle, and not the length of the sides, which, if lengthened out ever so far, would not affect the size of the angle, because the opening will only be the same part of a a great circle that it was of a small one.
Imagine two lines which cross each other as in figures 9 and 10. They will make four angles. These are right angles if they are equal, and they will be equal if one line is perpendicular to the line it crosses. If the angle be less than a right angle, it is called an acute angle; if more, it is called an obtuse angle. Acute means sharp, and obtuse means blunt.
21. Make an obtuse angle. (fig. 8.)
22. Make an acute angle with the opening turned upward, downward, to the right and to the left.
23. Make a triangle. (fig. 11.)