jawab kak no 31 - 35 plissssss

31. Un = n^2 + 3n
      U1= 1^2 + 3 x 1 = 4
      U2 = 2^2 + 3 x 2 = 4 + 6 = 10
      U3 = 3^2 + 3 x 3 = 9 + 9 = 18
      U4 = 4^2 + 3 x 4 = 16 + 12 = 28
      U5 = 5^2 + 3 x 5 = 25 + 15 = 40