Aritmatika u3=1 u6=10 brp kah suku ke 21

U3 = 1
a + 2b = 1

U6 = 10
a + 5b = 10

a + 5b = 10
a + 2b = 1   –
——————-
3b = 9
b = 9 : 3
b = 3

a + 2b = 1
a + 2 × 3 = 1
a + 6 = 1
a = 1 – 6
a = -5

U21 = a + 20b
U21 = -5 + 20 × 3
U21 = -5 + 60
U21 = 55

U3 = a+2b 
U6 = a+5b

Diketahui:
a+2b = 1
a+5b = 10

Eliminasikan:
a+2b = 1
a+5b = 10
__________ –
-3b = -9
b = 3

a+2b = 1
a+2(3) = 1
a+6 = 1
a = -5

U21: a+20b = ?

Jwab:
a+20b = -5+20(3) = -5+60 = 55

Suku 21 adalah: 55

Salam..
Smoga suksess ^^