Question

tentukan, 10 suku pertama barisan aritmatika berikut

a).-3,-6,-9,-12....
b). 4,16,64...
c). 2,4,8,16...
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Answer 1

Jawaban:

a. b = -6 -(-3) = -3

U10 = -3 + (9×(-3) = -30

S10 = 5((-3)+(-30) = 5×(-33) = -165

b. b = 16/4 = 4

U10 = 4×4^9 = 1.048.576

S10 = 4(4^10 - 1)/3 = 1.398.100

c. b = 4/2 = 2

U10 = 2×2^9 = 1.024

S10 = 2(2^10 -1)/1 = 2.046

Penjelasan :

rumus suku ke-n aritmatika

Un = a + (n-1)b

b = Un - U(n-1)

Sn = n/2 (a + Un)

rumus suku ke-n geometri

Un = ab^n-1

b = Un / U(n-1)

Sn = a(b^n -1)/b -1