2 soal tolong dengan caranya ya

9.
U1 = 3   = 3 x 1   = 3 x 1               = 3 x 1/2 x 1 x 2
U2 = 9   = 3 x 3   = 3 x (1+2)         = 3 x 1/2 x 2 x 3
U3 = 18 = 3 x 6   = 3 x (1+2+3)     = 3 x 1/2 x 3 x 4
U4 = 30 = 3 x 10 = 3 x (1+2+3+4) = 3 x 1/2 x 4 x 5

Un = 3 x 1/2 x (n) x (n-1)

U8 = 3 x 1/2 x 8 x 9
      = 108  buah


10.
Bilangan tanpa kekeliruan
= 1+ 2 + 3 + ....... + 75
= 1/2 x 75 x 76
=  2850

Yang keliru
= 2922 - 2850
= 72

(x) + (x+2) + (x+4) = 72
3x + 6 = 72
3x = 72 - 6
     = 66
x = 66 : 3
   = 22   (C)