1.tentukan rumus suku ke 5 dari barisan berikut! a.90,50,10,-30,... b.1,3,7,15,... c.2,5,10,17,...

a) a = 90
b = 50-90 = -40

U5 = 90 + (5-1) x -40
= 90 + (4 x -40)
= 90 + -160
= -70

b) a = 1
b = 3-1 = 1

U5 = 1 + (5-1) x 1
= 1 + (4 x 1)
= 1 + 4
= 5

c) a = 2
b = 5-2 = 3

U5 = 2 + (5-1) x 3
= 2 + (4 x 3)
= 2 + 12
= 14

a. Un = a + ( n - 1 ) b
U5 = 90 + ( 5 - 1 ) (-40)
= 90 + 4 (-40)
= 90 + (-160)
U5 = -70

b. U5 = 1 + ( 5 - 1 ) 2
= 1 + 4 × 2
U5 = 10

c. U5 = 2 + ( 5 - 1 ) 3
= 2 + 4 × 3
U5 = 18