Question #b6ffe
2 Answers
Two ways
Explanation:
We observe that these are the first few terms of a geometric sequence because the ratio of each term to the term before it is the same value ... -3.
For this sum,
the first term is
The common ratio is
Since
By the formula for summation
For this particular sum, we have
Add these up to get
Explanation:
#"the sum to n terms of a geometric series is"#
#•color(white)(x)S_n=(a(1-r^n))/(1-r)#
#"where a is the first term, r the common ratio and n the"#
#"number of terms"#
#"here " a=1, r=(-3)/1=9/(-3)=-3 ,n=6#
#rArrS_6=(1(1-(-3)^6))/(1-(-3)#
#color(white)(rArrS_6)=(1-729)/4=-182#