u1=5 u6=55 tentukan S16

Aritmatika (?)

U1 = a = 5
U6 = a + (n - 1) b = a + 5b = 55

a+5b = 55
5+5b = 55
    5b = 50
      b = 10

Sn = n/2 (2a + (n-1)b)
S16 = 16/2 (2x5 + (16-1)10)
S16 = 8 (10 + 150)
S16 = 1280