Write a formula...

Question

Write a formula for the general term (the nth term) of the geomteric sequence. Then use the formula for an to find a7, the seventh term of the sequence.

3, 15, 75, 375

 

NOTE: The system tells me it isn't 46875

Answer 1

For the geometric sequence 3, 15, 75, 375,..., the common ratio, r, is 5 since 15/3 = 5, 75/15 = 5, 375/75 = 5, etc.  

 

a₁ = 3

 

a_n = a₁r^n-1 = 3(5)^n-1

 

So, a₇ = 3(5)⁶ = 46875