Jawabanmu

2014-04-11T22:03:39+07:00
Bilangan pertama =  (2x + 1) 
Bilangan Terakhir = (2x + 50) 

S(50) = 50/2 * [(2x + 1) + (2x + 50)] 
4,275 = 25 * (2x + 1 + 2x + 50) 
4,275 = 25 * (2x + 2x + 1 + 50) 
4,275 = 25 * (4x + 51) 
4,275 = 100x + 1275 
4,275 - 1,275 = 100x 
3,000 = 100x 
30 = x.
rumusnya S(n) = n/2 * (a + b)
b = bilangan terakhir
a = bilangan pertama