## Algebra and Trigonometry 10th Edition

Published by Cengage Learning

# Chapter 11 - 11.6 - Counting Principles - 11.6 Exercises - Page 825: 73

36 lines.

#### Work Step by Step

Each line will be obtained by selecting two different points among the 9 points. The order in which the two points are selected is not important. So, it is a combination: $_9C_2=\frac{9!}{(9-2)!~2!}=\frac{9\times8\times7!}{7!~2}=36$

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