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b. Pada sebuah deret aritmetika, diketahui begin mathsize 14px style a equals 3 end stylebegin mathsize 14px style U subscript n equals 87 end style, dan begin mathsize 14px style U subscript 6 plus U subscript 7 equals 39 end style. Hitunglah begin mathsize 14px style S subscript n end style

  1. ...space 

  2. ...undefined 

M. Nasrullah

Master Teacher

Mahasiswa/Alumni Universitas Negeri Makassar

Jawaban terverifikasi

Jawaban

begin mathsize 14px style S subscript n equals 1.305 end style

Pembahasan

begin mathsize 14px style table attributes columnalign right center left columnspacing 0px end attributes row cell U subscript 6 plus U subscript 7 space end cell equals 39 row cell open parentheses a plus 5 b space close parentheses plus open parentheses a plus 6 b close parentheses end cell equals 39 row cell 2 a plus 11 b end cell equals 39 row cell 2 open parentheses 3 close parentheses plus 11 b end cell equals 39 row cell 11 b end cell equals cell 39 minus 6 end cell row cell 11 b end cell equals 33 row cell b space end cell equals cell space 3 end cell end table end style

begin mathsize 14px style table attributes columnalign right center left columnspacing 0px end attributes row cell U subscript n end cell equals 87 row cell a plus left parenthesis n minus 1 right parenthesis b end cell equals 87 row cell 3 plus left parenthesis n minus 1 right parenthesis 3 end cell equals 87 row cell left parenthesis n minus 1 right parenthesis 3 end cell equals cell 87 minus 3 end cell row cell n minus 1 end cell equals cell 84 over 3 end cell row n equals cell 28 plus 1 end cell row n equals 29 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 space n over 2 left parenthesis a space plus space U n right parenthesis end cell row cell S subscript n end cell equals cell 29 over 2 left parenthesis 3 plus 87 right parenthesis end cell row cell S subscript n end cell equals cell 29 over 2 cross times space 90 end cell row cell S subscript n end cell equals cell 29 cross times 45 end cell row cell S subscript n end cell equals cell 1.305 space end cell end table end style

Jadi, begin mathsize 14px style S subscript n equals 1.305 end style

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Pada deret aritmetika, apabila: b. a=−0,5danU12​=−33,5, carilah b dan S12​.

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