Question : If the 3rd and 9th term of a geometric series with a positive common ratio are -3 and -192 respectively, determine the value of the first term, a.
I was thinking that you have to find out r first so i did this :
an = a3 x r^n-1
a9 = -3 x r^3-1
-192 = -3r^2
/-3 /-3
64=r^2
r=8
Using this, I don't know how to find out the first term still.. I tried this:
a1 = -3x8^1-1
a1 = -3x8^0
I don't really know what to do at this point but if its 8^0 then thats 0 so the a1=-3 but the 3rd term is -3 :shock:
I was thinking that you have to find out r first so i did this :
an = a3 x r^n-1
a9 = -3 x r^3-1
-192 = -3r^2
/-3 /-3
64=r^2
r=8
Using this, I don't know how to find out the first term still.. I tried this:
a1 = -3x8^1-1
a1 = -3x8^0
I don't really know what to do at this point but if its 8^0 then thats 0 so the a1=-3 but the 3rd term is -3 :shock: