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Jumlah suku pertama dan ketiga suatu barisan geomt...

Jumlah suku pertama dan ketiga suatu barisan geomteri sama dengan 5, sedangkan jumlah suku ketiga dan suku kelima sama dengan 20. Suku pertama dan rasionya adalah ...

  1. 2 dan 1

  2. 2 dan 3

  3. -1 dan -2

  4. 1 dan 2

  5. 3 dan 2

Jawaban:

begin mathsize 14px style u subscript n equals a. r to the power of n minus 1 end exponent space space space u subscript 1 plus u subscript 3 equals 5 space space space space space space space space space space space space space space space space space space space space space u subscript 3 plus u subscript 5 equals 20 space space space a plus a r squared equals 5 space space space space space space space space space space space space space space space space space space space a r squared plus a r to the power of 4 equals 20 a open parentheses 1 plus r squared close parentheses equals 5 space space space space space space space space space space space space space space space space space a r squared open parentheses 1 plus r squared close parentheses equals 20 kemudian space kita space bagi fraction numerator a r squared open parentheses 1 plus r squared close parentheses over denominator a open parentheses 1 plus r squared close parentheses end fraction equals 20 over 5 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space r squared equals 4 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space r equals plus-or-minus 2 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space r equals 2 rightwards arrow a open parentheses 1 plus r squared close parentheses equals 5 space space space space space space space space space space space space space space space space space r equals negative 2 rightwards arrow a open parentheses 1 plus r squared close parentheses equals 5 space space space space space space space space space space space space space a open parentheses 1 plus 2 squared close parentheses equals 5 space space space space space space space space space space space space space space space space space space space space space space space space space space space a open parentheses 1 plus open parentheses negative 2 close parentheses squared close parentheses equals 5 space space space space space space space space space space space space space space space space space space space space space space space space a equals 1 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space a open parentheses 1 plus 4 close parentheses equals 5 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space a equals 1 jadi comma space a equals 1 space dan space r equals 2 comma space atau space a equals 1 space dan space r equals negative 2 end style 

Jadi. jawaban yang tepat adalah D.   

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