an=a1*(r)^(n-1)
a3=-18=a1*(r)^(3-1)=a1*r^2
a6=486=a1*(r)^(6-1)=a1*r^5
a6/a3=(a1*r^5)/(a1*r^2)=r^3=486/-18=-27
r^3=-27
r=-3
math
-18=a1*r^2
-18=a1*(-3)^2
-18=a1*9
-2=a1
sum of first n terms of geo is
[tex] \frac{a_1(1-r^n)}{1-r} [/tex]
r=-3
a1=-2
n=6
[tex] \frac{-2(1-(-3)^6)}{1-(-3)} [/tex]
[tex] \frac{-2(1-729)}{1+3} [/tex]
[tex] \frac{-2(-728)}{4} [/tex]
[tex] \frac{1456}{4} [/tex]
364 is the sum of first 6 terms
