# Determine Sn for the geometric series? f(1)=2, r=-2, n=12

##### 1 Answer

Jun 21, 2018

#### Explanation:

#"the sum to n terms of a geometric sequence is"#

#•color(white)(x)S_n=(a(r^n-1))/(r-1)#

#"where a is the first term and r the common ratio"#

#"here "a=2,r=-2" and "n=12#

#S_(12)=(2((-2)^(12)-1))/(12-1)#

#color(white)(xxxxxx)=(2(4096-1))/11=8190/11#