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