116. How many lines can divide a plane into 5 parts?
116. Two lines can divide the plane only into 3 or 4 parts (see Fig. 15). Three lines can divide the plane only into 4, 6, and 7 parts (see Fig. 16). Four lines can divide the plane into 5 parts only if these lines are parallel (see Fig. 17). It is obvious that with any arrangement of five or more lines, the number of parts of the plane will be more than five.
![](https://cdn.mathpix.com/cropped/2024_05_21_a21e90374409a05a4ea7g-25.jpg?height=266&width=1002&top_left_y=395&top_left_x=490)

Fig. $\quad 16$



![](https://cdn.mathpix.com/cropped/2024_05_21_a21e90374409a05a4ea7g-25.jpg?height=324&width=1308&top_left_y=958&top_left_x=404)