tiga buah bilangan membentuk barisan aritmatika dengan beda tiga

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Dengan Konsep barisan geometri:

Misalkan: Berikut ini yakni barisan aritmatika:

begin mathsize 14px style straight U subscript 1 equals straight a end style maka:

begin mathsize 14px style table attributes columnalign right center left columnspacing 0px end attributes row cell straight U subscript 2 end cell equals cell straight a plus 3 end cell row cell straight U subscript 3 end cell equals cell straight a plus 3 plus 3 equals straight a plus 6 end cell end table end style

Jika suku kedua dikurang 1, maka terbentuklah barisan geometri yaitu:

begin mathsize 14px style straight U subscript 1 equals straight a end style

straight U subscript 2 table attributes columnalign right center left columnspacing 0px end attributes row blank equals blank end table table attributes columnalign right center left columnspacing 0px end attributes row blank blank straight a end table table attributes columnalign right center left columnspacing 0px end attributes row blank blank plus end table table attributes columnalign right center left columnspacing 0px end attributes row blank blank 2 end table straight U subscript 3 table attributes columnalign right center left columnspacing 0px end attributes row blank equals blank end table table attributes columnalign right center left columnspacing 0px end attributes row blank blank straight a end table table attributes columnalign right center left columnspacing 0px end attributes row blank blank plus end table table attributes columnalign right center left columnspacing 0px end attributes row blank blank 3 end table table attributes columnalign right center left columnspacing 0px end attributes row blank blank plus end table table attributes columnalign right center left columnspacing 0px end attributes row blank blank 3 end table table attributes columnalign right center left columnspacing 0px end attributes row blank equals blank end table table attributes columnalign right center left columnspacing 0px end attributes row blank blank straight a end table table attributes columnalign right center left columnspacing 0px end attributes row blank blank plus end table table attributes columnalign right center left columnspacing 0px end attributes row blank blank 6 end table

Maka:

table attributes columnalign right center left columnspacing 0px end attributes row cell straight U subscript 1 plus straight U subscript 2 plus straight U subscript 3 end cell equals 14 row cell straight a plus straight a plus 2 plus straight a plus 6 end cell equals 14 row cell 3 straight a plus 8 end cell equals 14 row cell 3 straight a end cell equals 6 row straight a equals 2 end table

subtitusi nilai a ke dlm suku pertama & kedua pada barisan geometri

table attributes columnalign right center left columnspacing 0px end attributes row cell straight U subscript 1 end cell equals 2 row cell straight U subscript 2 end cell equals cell a plus 2 equals 2 plus 2 equals 4 end cell end table

sehingga rasionya yaitu

table attributes columnalign right center left columnspacing 0px end attributes row straight r equals cell straight U subscript 2 over straight U subscript 1 end cell row blank equals cell 4 over 2 end cell row blank equals 2 end table

Jadi, Rasio barisan geometri di atas adalah 2.

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