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Jawaban:

11. a. U15 = ....?

maka ,

a = 1

b = 2–1 = 1

Un = a +(n –1)b

U15 = 1 + (15–1)1

= 1+(14)1

= 1+14

= 15

b. a = 4

b = 1–4 = –3

Un = a +(n –1)b

U18 = 4+(18–1)–3

= 4+(17)–3

= 4+(–51)

= 4–51 = –47

12. U4 = 19

U7 = 31

maka,

U4 = a + 3b = 19

U7 = a + 6b = 31

–––––––––– –

-3b = –12

b = 12/3 = 4

=> a + 3b = 19

a + 3(4) = 19

a + 12 = 19

a = 19–12

a= 7

a = 7

b = 4

maka, U50 =...?

Un = a + (n-1)b

U50 = 7 + (50–1)4

= 7+(49)4

= 7+(196)

= 203

semoga membantu