Jawabanmu

2014-03-18T20:03:52+07:00
U1=25
U4=49
S10=?

U1= U1 + (n-1) b
25= 25 + (1-1)b
25=25+b

U4= U1 + (n-1) b
49= 25 + (4-1) b
49= 25 + 3b

49=25 + 3b
25=25 + b
                           -
--------------------------
24=2b
12=b 

S10= n/2(2U1 + (n-1) b)
s10= 10/2 (2.25 + (10-1) 12)
s10= 5 (50 + 108)
s10= 5 (158)
s10= 790
1 5 1
2014-03-18T20:25:06+07:00
U1=25
U4=49
S10...?

U1=25 ⇒ a+b=25
U4=49 ⇒ a+3b=49

a+b=25
a+3b=49
________ _
    -2b= -24
       b=12
       a=13 (masukkan nilai b lalu 25-nilai b = a)

S10=n/2 (2a + (n-1)xb)
      = 10/2 (2x13 + (10-1)x12)
      = 5 (26 + 108)
      =5 x 134
      = 670