tolong jawabin dong, pakai cara yaaa thx:)))

U1 = 4. ===> a = 4
U2 = 9
U3 = 16
U4= 25
4, 9, 16, 25,...
....5,..7,...9.
.......2...2..
Un = a + (n-1)b1/1! + (n-1)(n-2)b2/2!
un = 4 + (n-1)5/1! + (n^2 -3n +2)2/2!
Un = 4 +5n -5 + n^2 -3n +2
Un = n^2 +2n +1
Un = (n+1)^2... jawaban (B)