Question

Evaluate 7 Σ n=1 2(-2)^n-1.

Answer 1

86

Explanation:

I assume the question is
`\sum_(n=1)^(7) 2(-2)^(n-1)`

7: 2(-2)^6 = 128

6: 2(-2)^5 = -64

5: 2(-2)^4 = 32

4: 2(-2)^3 = -16

3: 2(-2)^2 = 8

2: 2(-2)^1 = -4

1: 2(-2)^0 = 2

128 - 64 + 32 - 16 + 8 - 4 + 2 = 86