Write the expression without using sigma notation, and then find the sum

Question

Write the expression without using sigma notation, and then find the sum.

Write the expression without using sigma notation, and then find the sum.

(a)    5	(1 − n2)
n = 1

(b)    6	(−1)n2n − 3
n = 3

Answer 1

1-1^2 = 0

1-2^2 = -3

1-3^2 = -8

1-4^2 =-15

1-5^2 =-24

sum = 0-3-8-15-24 = -50

(-1)^n(2)^n-3

signs alternate, it's a geometric series with common ratio -2

for n=3 -1

for n =4 2

for n = 5 -4

for n = 6 8

sum =-1+2-4+8 = 5