1+4+7+10+..+52 tlong pake cara

1 + 4 + 7 + 10 + ... + 52

U₁ = a = 1
  b = 4 -1 
     = 3

Un = a + (n - 1) x b
52 = 1 + (n - 1) x 3
52 = 1 + 3n - 3
52 = -2 + 3n
54 = 3n
  n = 18

Sn = n/2 x (a + Un)
S₁₈ = 18/2 x (1 + 52)
      = 9 x 53
      = 477

semoga jelas dan membantu ya