Find the sum of the following series :

Question

a) 1 - 1/¡Ì2 1/2 - 1/2¡Ì2 ¡­to 20 terms.

Answer 1

apparently you have

a = 1
r = -1/√2

S20 = a(1-r^20)/(1-r) = 1023/(512(2+√2))