First of all, it is necessary to make it clear that the infected person is infected with 2 people, and then ***3 infected people (1 to the third power).

On the 3rd, there were 3 original infected people plus 6 new infected people and 9 * * * (3 to the second power).

Therefore, the total number of infected people increased geometrically, with a common ratio of 3, and the first term was 1.

On February 6, the total number of infected people reached the fifth power of 3, which was 243, exceeding 100.