Question

U1 =3 U2=9 U3 = 18 U4 = 30 U7 = ?(banyak batang korek apinya untuk pola segitiga ke 7 ?)

Answer 1

Verified answer

Mapel : Matematika
Kelas : IX SMP
Bab : Barisan dan Deret

Pembahasan :
3 , 9 , 18 , 30
...6....9.....12....
.......3.....3.......

2A = Konstanta
2A = 3
A = 3/2

3A + B = Beda
3A + B = 6
3(3/2) + B = 6
9/2 + B = 6
B = 6 - (9/2)
B = 3/2

A + B + C = Suku pertama
(3/2) + (3/2) + C = 3
3 + C = 3
C = 0

Gunakan Rumus Fungsi Kuadrat
Un = An² + Bn + C
Un = 3/2 n² + 3/2 n + 0
Un = 3/2 n(n + 1)
U7 = 3/2 . 7(7 + 1)
U7 = 21/2(8)
U7 = 84