Jawabanmu

2014-03-31T19:23:09+07:00
U2 = a+b  = 19
u5 = a+4b = 31 eliminasi
          -3b = -12
jadi b=4 , a=15

S24 = n/2 (2a+(n-1)b)
       = 24/2 (2.15 + (24-1)4)
       = 12 (30+ 23.4)
       = 12. 122
       = 1464