Tolong jawabya soal ini aku kasih 11 poin

Penyelesaian:

a. barisan bilangan: 1 + 2 + 3 + 4 + … + 99
a = 1
b = 1

Un = a + (n-1)b
99 = 1 + (n-1)(1)
99 = n

Sn = n/2 (2a + (n-1)b)
= 99/2 (2(1) + (99-1)1)
= 99/2 (2 + 98)
S99 = 4,950

b. barisan bilangan: 1 – 2 + 3 – 4 + 5 – … – 100
dapat di pecah menjadi 2 barisan bilangan:

barisan bilangan beda positif: 1 + 3 + 5 + … + 99
a = 1
b = 2

Un = a + (n-1)b
99 = 1 (n-1)2
99 = 1 + 2n – 2
n = 50

Sn = n/2 (2a + (n-1)b)
= 50/2 (2(1) + (50-1)(2)
= 25 (2 + 98)
Sb1 = 2,500

barisan bilangan beda negatif: – 2 – 4 – 6 – 8 – … – 100
a = -2
b = -2

Un = a + (n-1)b
-100 = -2 + (n-1)(-2)
-100 = -2 -2n + 2
n = 50

Sn = n/2 (2a + (n-1)b)
= 50/2 (2(-2) + (50-1)(-2)
= 25 (-4 – 98)
= 25 (-102)
S2 = -2,550

S1 + S2 = 2,500 – 2,550 = -50

c. barisan bilangan:-100 – 99 – 98 – … + 50
a = -100
b = 1

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

Sn = n/2 (2a + (n-1)b)
= 151/2 (2(-100) + (151-1)1)
= 151/2 (-200 + 150)
= 151/2 (-50)
Sn = -3,775