suatu barusan aritmatika diketahui U4 + U6 = 28 dan U7 + U10 = 42. Tentukan suku pertama, beda, dan U15

Mapel : Matematika
Bab : barisan dan deret

U4 + U6 = 28
a + 3b + a + 5b = 28
2a + 8b = 28

U7 + U10 = 42
a + 6b + a + 9b = 42
2a + 15b = 42

Eliminasi :
2a + 8b = 28
2a + 15b = 42
___________ _
-7b = -14
b = -14/-7
b = 2

2a + 8b = 28
2a + 8(2) = 28
2a + 16 = 28
2a = 28 - 16
2a = 12
a = 6

U15 = a + 14b
U15 = 6 + 14(2)
U15 = 6 + 28
U15 = 34

Jadi
a = 6
b = 2
U15 = 34