Answer: -129
Step-by-step explanation:
Given the sequence {-3, 6, -12, 24, ... }, we can see that the first term (a) is -3 and the ratio (r) is [tex]\dfrac{6}{-3} = -2[/tex].
Input those values into the Sum formula:
[tex]S_n=\dfrac{a(1-r^n)}{1-r}\\\\S_7=\dfrac{-3(1-(-2)^7)}{1-(-2)}\\\\.\quad=\dfrac{-3(1-(-128))}{1+2}\\\\.\quad=\dfrac{-3(1+128)}{3}\\\\.\quad=\dfrac{-3(129)}{3}\\\\.\quad=-129[/tex]
