a. 1+3+5+7+9+...+99 b. 1-2+3-4+5-6+7-8+...-100 c. -100-99-98-...-2-1-0+1+2+...+48+49+50

Bab Pola Bilangan
Matematika SMP Kelas VII

a] 1 + 3 + 5 + ... + 99 → deret bilangan kuadrat
= ((1 + 99)/2)²
= ((100)/2)²
= 50²
= 2.500

b] 1 - 2 + 3 - 4 + ..... + 99 - 100
= bilangan terakhir/2 → berlaku jika soal seperti di atas
= -100/2
= -50

c] -100 - 99 - 98 - ... - 2 - 1 - 0 + 1 + 2 + .... + 50 =

-50 + 50 = 0
- 49 + 49 = 0
.
.
-1 + 1 = 0
0

sisa
-100 - 99 - 98 - .... - 51 = ?

-100 - 51 = -151
-99 - 52 = -151
.
.
((- 51 - ( - 100) + 1 ) / 2) x (-151)
= ((-51 + 100 + 1)/2) x (-151)
= (50/2) x (-151)
= 25 x (-151)
= -3.775