Pakai cara #12 poin

Matematika
Pola Bilangan VII SMP

Pembahasan :
Un = 99
2n – 1 = 99
2n = 100
n = 50

1 + 3 + 5 + … + 99
= n²
= 50²
= 2500

————————————————
1 – 2 + 3 – 4 + … – 100
= (1 – 2) + (3 – 4) + … + (99 – 100)
= -1 – 1 – … – 1
= -(1 + 1 + … + 1)
= -(100/2)
= -50

————————————————
Un = 50
a + (n – 1)b = 50
-100 + (n – 1)1 = 50
n – 101 = 50
n = 151

-100 – 99 – … + 50
= n/2(a + Un)
= 151/2(-100 + 50)
= 151/2(-50)
= -3775