Jawabanmu

2014-02-08T15:53:22+07:00
21,24,27,30,33,36,39,42,45,,48,51,54,57,60,63,............500
jikakelipatan 3 antar 400,500
caranya 
Bilangan itu adalah : 402, 405, 408, ....., 498 
a = 402, b = 3 

Un = a + (n - 1)b 
498 = 402 + (n - 1)3 
498 = 402 + 3n - 3 
498 = 399 + 3n 
3n = 498 - 399 
3n = 99 
n= 33 

Sn = 1/2 n (a + Un) 
.....= 1/2 x 33 x (402 + 498) 
.....= 16,5 x 900 
Sn = 14.850
2014-02-08T17:41:39+07:00