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Diketahui jumlah suku pertama suatu deret aritmetika adalah . Suku ke- dari deret tersebut adalah ....

Diketahui jumlah undefined suku pertama suatu deret aritmetika adalah begin mathsize 14px style S subscript n equals 1 half n left parenthesis 3 n minus 17 right parenthesis end style. Suku ke-undefined dari deret tersebut adalah ....

  1. begin mathsize 14px style 3 n minus 10 end style 

  2. begin mathsize 14px style 3 n minus 8 end style 

  3. begin mathsize 14px style 3 n minus 6 end style 

  4. begin mathsize 14px style 3 n minus 4 end style 

  5. begin mathsize 14px style 3 n minus 2 end style 

Jawaban:

begin mathsize 14px style table attributes columnalign right center left columnspacing 0px end attributes row cell S subscript n end cell equals cell n over 2 left parenthesis a plus U subscript n right parenthesis end cell row cell 1 half n left parenthesis 3 n minus 17 right parenthesis end cell equals cell n over 2 left parenthesis a plus U subscript n right parenthesis end cell row cell n over 2 left parenthesis 3 n minus 17 right parenthesis end cell equals cell n over 2 left parenthesis a plus U subscript n right parenthesis end cell row cell 3 n minus 17 end cell equals cell a plus U subscript n end cell row cell U subscript n end cell equals cell 3 n minus 17 minus a... left parenthesis 1 right parenthesis end cell end table end style

begin mathsize 14px style table attributes columnalign right center left columnspacing 0px end attributes row cell S subscript n end cell equals cell 1 half n left parenthesis 3 n minus 17 right parenthesis end cell row cell S subscript 1 end cell equals cell 1 half open parentheses 1 close parentheses left parenthesis 3 open parentheses 1 close parentheses minus 17 right parenthesis end cell row a equals cell 1 half left parenthesis 3 minus 17 right parenthesis end cell row a equals cell 1 half open parentheses negative 14 close parentheses end cell row a equals cell negative 7 end cell end table end style

Suntitusi nilai begin mathsize 14px style a equals negative 7 end style ke persamaan 1

begin mathsize 14px style table attributes columnalign right center left columnspacing 0px end attributes row blank blank U end table table attributes columnalign right center left columnspacing 0px end attributes row blank blank cell blank subscript n end cell 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 cell 3 n minus 17 minus a end cell end table U table attributes columnalign right center left columnspacing 0px end attributes row blank blank cell blank subscript n end cell 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 cell 3 n minus 17 minus open parentheses negative 7 close parentheses end cell end table table attributes columnalign right center left columnspacing 0px end attributes row blank blank space end table table attributes columnalign right center left columnspacing 0px end attributes row blank blank cell U subscript n end cell 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 cell 3 n minus 10 end cell end table end style

Jadi, jawaban yang tepat adalah A

 

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