1-1+1-1+1-1+......+n সংখ্যক পদের যোগফল হবে-
A
1
B
[1+(-1)n]
C
12[1-(-1)n
Correct Answer: 12[1-(-1)n
a = 1r = - 11 = - 1Sn = a(1 - rn)1 - r = 1{1 - ( - 1)n}1 - ( - 1) = 1 - ( - 1)n2 = 12{1 - ( - 1)n}