suatu barisan aritmetika diketahui U4 + U6 = 28 dan U7 + U10 = 42. Tentukan; a. suku pertama b. beda c. U15

U4 + U6 = 28 U4 + U4 + 2b = 28
U7 + U10 = 42 U4 + 3b + U4 + 6b = 42

2.U4 + 2b = 28
2.U4 + 9b = 42
————————— -
-7b = - 14
(b) b = 2

substitusi b ke persamaan U4 + U6 = 28
2.U4 + 2(2) = 28
2.U4 + 4 = 28
2.U4 = 24
(a) U4 = 24/2 = 12

U15 = U4 + 11b
U15 = 12 + 11(2) = 12 + 22
(c) U15 = 34