suatu barisan aritmatika diketahui U10= -11 dan U5= -1. Nilai U15 barisan tersebut adalah... tolong pembahasannya...

U5= -1
U10= -11
b= -11 -(-1)/10-5= -11 + 1/10-5= -10/5= -2

U15=U10 + 5b
U15= -11 + 5 • -2
U15= -11 + -10= -21

Smoga membantu

Cara lain... ↓↓

U5 = a + 4b = -1
U10 = a + 9b = -11
______________-
-5b = 10
b = -2

a + 4b = -1
a = -1 - 4(-2)
a = 7

U15 = a + 14b
U15 = 7 + 14(-2)
U15 = 7 - 28
U15 = -21

Semoga berguna +_+