Question

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

Bantu jawab yaaa... sekalian caranya...

Answer 1

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

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

1 + 3 + 5 + 7 + ... + 99 = n²
1 + 3 + 5 + 7 + ... + 99 = 50²
1 + 3 + 5 + 7 + ... + 99 = 2500

————————————————
1 - 2 + 3 - 4 + ... - 100
= -1 - 1 - 1 - 1 - ... - 1
= -(1 + 1 + ... + 1)
= -(100/2)
= -50

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

-100 - 99 - 98 - ... + 50
= S151
= 151/2(-100 + 50)
= 151/2(-50)
= -3775