Suku ke-50 dari barisan 20, 17, 14, 11, 8 adalah

Barder

a = 20
b = 17-20 = -3

Maka
U50
= 20 + 49(-3)
= 20 - 147
= -127

a = U1 = 20
b = U2 - U1
b = 17 - 20
b = - 3

Un = a + ( n - 1 ) b
U50 = 20 + ( 50 - 1 ) - 3
U50 = 20 + ( 49 ) - 3
U50 = 20 + ( - 147 )
U50 = - 127 ✔️

Semoga bermanfaat.....
-Prisco