Penjelasan dengan langkah-langkah:

1)

a= -6

u8 = a + 7b = 50

-6 + 7b = 50

b = 8

a = 2

c = 18

d = 26

e = 34

jadi = 80

2)

u3 = a + 2b = 8

u6 = a + 5b = 17

eliminasi:

-3b = -9

b = 3

subs b = 3 ke salah satu persamaan:

a + 2(3) = 8

a = 2

Jadi u22 = 2 + (22-1)3

u22 = 65

3)

cari dulu 104 itu baris ke berapa:

un = a + (n-1)b

104 = 4 + (n-1)5

104 = 4 + 5n - 5

n = 21

oh ternyata baris ke 21. jadi masukin ke rumus sn:

s21 = 21/2 (2×4 + (20)5)

s21 = 1134

4)

diket :

a = 8

u5 = 648

s3...?

jawab:

cari rasio dulu:

648 = 8r^4

81 = r^4

r = 3

sn = a(r^n - 1)/r-1

s3 = 8(3^3 - 1)/3-1

s3 = 8(26)/2

s3 = 4(26)

s3 = 104 cm

5)

rasio = u2/u1 = u3/u2

(a-1)/(a+2)=(a-7)/(a-1)

kali silang dapet

a = -5

rasionya:

(-5+2), (-5-1), (-5-7)

-3, -6, -12

-6/-3 = 2

rasio = 2

6)

rasio = 1/3

a = 3

maka u5= 3(1/3)^4

u5 = 3(1/81)

u5 = 1/27