60, 55, 50, 45, ..... tentukan 15 suku pertama

60, 55, 50, 45, ...

Un = a + (n-1) b

a = 60

b = 55-60
b = -5

Rumus =
Un = 60 - 5n + 5
Un = 65 - 5n

U5 = 65 - 5 x 5
U5 = 40

U6 = 65 - 5 x 5
U6 = 35

Begitu seterusnya, hingga menghasilkan barisan bilangan =

60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 0, -5, -10, -15, - 20, -25, -30, ...