Suatu barisan aritmetika U-3+U-7=56 dan u6+u10=86 , maka suku ke4 adalah... beserta caranya .....

U3 = a + 2b
U7 = a + 6b
U6 = a + 5b
U10 = a + 9b

a + 2b + a + 6b = 56
2a + 8b = 56

a + 5b + a + 9b = 86
2a + 14b = 86

2a + 8b = 56
2a + 14b = 86
____________ _
6b = 30
b = 30/6 = 5

2a + 8(5) = 56
2a = 56 - 40 = 16
a = 16/2 = 8

U4 = a + 3b
U4 = 8 + 3(5)
U4 = 8 + 15 = 23