Question

find the sum of the series 2+6+18+....+486

Answer 1

a = 2
d = 6-2 = 4
a n= 486
n= ?

a n = 486
a+(n-1)d = 486
=> 2+(n-1)4 = 486
=> 4n-4= 484
dividing by 4
n-1=121
n=122

S 122= n/2(a+a n) = 122/2(2+486) = 61*488 = 29768