dari barisan aritmetika U3+U5=20 dan U7=19,beda barisan itu adalah??

u3 + u5 = 20
a + (3 - 1)b + a + (5 - 1)b = 20
a + 2b + a + 4b = 20
2a + 6b = 20 ....(1)

u7 = 19
a + (7 - 1)b = 19
a + 6b = 19 ....(2)

pers (1) dan (2)

2a + 6b = 20
a + 6b = 19
____________-
a = 1

a + 6b = 19
1 + 6b = 19
6b = 19 - 1
6b = 18
b = 18/6
b = 3

maka beda barisan = 3