The number of tribbles that were on the starship after the 7th night is equal to 729 tribbles.
In Mathematics and Geometry, the nth term of any geometric sequence can be determined by using the following formula:
![a_n=a_1(r)^(n-1)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/6v3rfhe5z7jrml57fnstj1iac4v6g2j3cw.png)
Where:
is the nth term of any geometric sequence.- r represents the common ratio.
represents the first term of any geometric sequence.
Based on the information provided about the number of tribbles, we have the following geometric series;
1, 3, 9, ......
For the common ratio, we have;
Common ratio, r = 3/1 = 9/3
Common ratio, r = 3.
Now, we can write an explicit equation for the nth term of this geometric sequence;
![a_n=a_1(r)^(n-1)\\\\a_n=1(3)^(n-1)\\\\a_7=(3)^(7-1)\\\\a_7=3^6\\\\a_7=729\;tribbles](https://img.qammunity.org/2020/formulas/mathematics/middle-school/b0vf52sca8zr3tufm28ylhn14l53c2yzcy.png)