Jawabanmu

2014-06-12T18:35:46+07:00
Sn=n/2(U1+Un)
S10=10/2 ( (5×1-3)+(5×10-3)
S10=5 (2+47)
S10=245
2014-06-12T18:39:25+07:00
UN = 5n-3 . A = 5.1-3 = 2 , b=5 , n=10

Sn = 1/2 n (a + Un)
= 1/2 n (a + a + (n-1)b) 
= 1/2 n (2a + (n-1)b) 
S10 = 1/2. 10 (2.2 + 9.5) 
= 5 x (4 + 45) 
= 5 x 49 
S10 = 245