Tolong jawab yaa... 1. 1+2+3+.......+50= 2.1+3+5+......+15= 3.1+3+5+.....+99

Mapel : Matematika
Kelas : VII SMP
Bab : Aritmatika dasar

Pembahasan :
1 + 2 + 3 + ... + 50 = n/2(a + Un)
1 + 2 + 3 + ... + 50 = 50/2(1 + 50)
1 + 2 + 3 + ... + 50 = 25(51)
1 + 2 + 3 + ... + 50 = 1275

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Un = 15
2n - 1 = 15
2n = 16
n = 8

1 + 3 + 5 + ... + 15 = n²
1 + 3 + 5 + ... + 15 = 8²
1 + 3 + 5 + ... + 15 = 64

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

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

1)
a = 1
b = 1
n = 50

Sn = 1/2(n)[2a + (n - 1)b]
S50 = 1/2(50)[2(1) + (50 - 1) × 1]
S50 = 25 × [2 + 49 × 1]
S50 = 25 × [2 + 49]
S50 = 25 × 51
S50 = 1275

2)
a = 1
b = 2
n = 8
Sn = 1/2(n)[2a + (n - 1)b]
S8 = 1/2(8)[2(1) + (8 - 1) × 2]
S8 = 4 × [2 + 7 × 2]
S8 = 4 × [2 + 14]
S8 = 4 × 16
S8 = 64

3)
a = 1
b = 2
n = 100/2 = 50
Sn = 1/2(n)[2a + (n - 1)b]
S50 = 1/2(50)[2(1) + (50 - 1) × 2]
S50 = 25 × [2 + 49 × 2]
S50 = 25 × [2 + 98]
S50 = 25 × 100
S50 = 2500