Question

Evaluate 7 sigma notation n=1 2(-2)^n-1

Answer 1

the answer is D .86

Explanation:

Answer 2

This is a geometric of the form:

a(n)=2(-2)^(n-1)

And the sum of any geometric sum is:

s(n)=a(1-r^n)/(1-r) in this case:

s(n)=2(1-(-2^n))/(1--2)

s(n)=2(1-(-2^n))/3 so

s(7)=2(1-(-2^7))/3

s(7)=2(1--128)/3

s(7)=2(129)/3

s(7)=86