What is the 6th term of this geometric sequence?

5, –15, 45, –135…

3645 First we have to know the type of this sequenceso it is clear that the sequence is not increasing with a constant value so I think it is geometric sequence and to make sure If we divide 
brainliest??

A geometric series has the general formula for calculating the next number as follows 

Series is 5, 15 , 45 , T4 , T5 , T6 
Next Term (or nth term) = ar^n-1 

a = first term, i.e. 5 
r = common ratio i.e. 3 (as 15/5=3 and 45/15=3 so this must be a common ratio all through) 
n = the next terms we're to calculate 
as you already have 1st , 2nd and 3rd terms..then the next one is 4th then 5th and 6th. 

therefore n= 4 

substituting now 
T4= ar^n-1 
= 5*3^4-1 
= 5*3^3 
= 5*27 
T4 = 135 

T5= ar^n-1 
= 5*3^5-1 
= 5*3^4 
= 5*81 
T5 = 405 

T6= ar^n-1 
= 5*3^6-1 
= 5*3^5 
= 5*243 
T6= 1215 

Therefore whole series is 5, 15, 45, 135, 405, 1215 withe the last 3 being your required ones.