Question

Find the sum of the geometric sequence –3, 15, –75, 375, … when there are 8 terms and select the correct answer below.

–195,312
195,312
292,968
–292,968

Answer 1

Hello,

Answer B


`(-3)*(-5)^0\\ +(-3)*(-5)^1\\ +(-3)*(-5)^2\\ +(-3)*(-5)^3\\ +...\\ +(-3)*(-5)=\\\\ =(-3)*(1+(-5)+(-5)^2+(-5)^3+...+(-5)^7)\\ =-(3)* (1-(-5)^8)/(1-(-5)) \\ =-3* (1-5^8)/(6) \\\\ \boxed{=195312}\\`