3+6+9+12+...+99 Tolong pake caranya?

Deret Aritmatika
------------------------

Cara Menjawab :
3 + 6 + 9 + 12 + ... + 99
Maka,
a = 3
b = 6 - 3 = 3

Un = 99
a + (n - 1) b = 99
3 + (n - 1) 3 = 99
3 + 3n - 3 = 99
3n = 99
n = 99/3
n = 33

S33 = 1/2 n (a + U33)
S33 = 1/2 (33) (3 + 99)
S33 = 33 × 102/2
S33 = 33 × 51
S33 = 1683 --> Ini jawabannya

Semoga bisa bermanfaat
HHNS

Bab Pola Bilangan
Matematika SMP Kelas VII

3 + 6 + 9 + 12 + ... + 99 =

3 + 99 = 102
6 + 96 = 102
9 + 93 = 102
.
.
30 + 72 = 102
                ------ +
               1.020

33 + 69 = 102
36 + 66 = 102
39 + 63 = 102
42 + 60 = 102
45 + 57 = 102
48 + 54 = 102
              -------- +
                612
51

jumlahkan = 1.020 + 612 + 51 = 1.683