Question

Q1: Sum to (2n+1) terms the series 1 – 2 + 3 – 4 + ……
Q2: Show that 1 – 3 + 5 – 7 + …… to n terms = (‐1)n+1n.

Answer 1

a = 1 -2
d = 3 -4 -1 + 2
= 5 - 5
= o
Sn = n/2 { 2a + (n -1) d }
=( 2n + 1)/2 { 2 (1 -2) }
= - (2n + 1)