Question

Tentukan jumlah barisan berikut.
a. 30 bilangan cacah pertama
b. 28 bilangan ganjil pertama
c. 25 bilangan asli genap pertama.

Answer 1

A)
30 bilangan cacah pertama
0,1,2,3.....,Un
a = 0
U2 = 1
b = U2 - U1 = 1 - 0 = 1
Sn = n(2a+(n-1)b)/2
S30 = 30(2(0)+29(1))/2
S30 = 15(29) = 435

B)
28 bil. Ganjil pertama
1,3,5,7,...,un
a = 1
U2 = 3
b = 3 - 1 = 2
Sn = n(2a+(n-1)b)/2
S28 = 28(2(1) + 27(2))/2
S28 = 14(2 + 54)
S28 = 14(56) = 784

C)
25 bil. Asli Genap pertama
2,4,6,8,10,....,un
a = 2
Un = 4
b = 4 - 2 = 2
Sn = n(2a + (n-1)b)/2
S25 = 25(2(2) + 24(2)) /2
S25 = 25(26(2))/2
S25 = 25(26) = 650