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Perhatikan bangun datar berikut ini! Koordinat titik berat bangun datar yang diarsir adalah ….

Perhatikan bangun datar berikut ini!

Koordinat titik berat bangun datar yang diarsir adalah ….

  1. begin mathsize 14px style open parentheses 5 over 6 R comma blank fraction numerator 7 over denominator 3 pi end fraction R close parentheses end style 

  2. begin mathsize 14px style open parentheses 5 over 6 R comma blank fraction numerator 1 over denominator 3 pi end fraction R close parentheses end style 

  3. begin mathsize 14px style open parentheses 1 over 6 R comma blank fraction numerator 7 over denominator 3 pi end fraction R close parentheses end style 

  4. begin mathsize 14px style open parentheses 1 half straight pi R comma blank 4 over 15 R close parentheses end style     

  5. begin mathsize 14px style open parentheses 1 half R comma blank fraction numerator 14 over denominator 15 pi end fraction R close parentheses end style   

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D. Kusumawardhani

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Jawaban terverifikasi

Jawaban

jawaban yang tepat adalah E.

jawaban yang tepat adalah E.

Pembahasan

Bangun datar tersebut berupa setengah lingkaran besar (dengan jari-jari R) yang dipotong oleh setengah lingkaran kecil (dengan jari-jari ).Agar mempermudah perhitungan koordinat tiap bangun, gambarkan garis-garisnya → Bangun 1 → Bangun 2 Titik berat bangun yang diarsir dapat dicari dengan cara Sementara itu titik berat pada sumbu y adalah Dengan demikian jawaban yang tepat adalah E.

Bangun datar tersebut berupa setengah lingkaran besar (dengan jari-jari R) yang dipotong oleh setengah lingkaran kecil (dengan jari-jari begin mathsize 14px style 1 half straight R end style). Agar mempermudah perhitungan koordinat tiap bangun, gambarkan garis-garisnya

→ Bangun 1

begin mathsize 14px style table attributes columnalign right center left columnspacing 0px end attributes row blank blank A end table table attributes columnalign right center left columnspacing 0px end attributes row blank blank cell blank subscript 1 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 1 half end cell end table table attributes columnalign right center left columnspacing 0px end attributes row blank blank pi end table table attributes columnalign right center left columnspacing 0px end attributes row blank blank cell r subscript 1 end cell end table table attributes columnalign right center left columnspacing 0px end attributes row blank blank cell blank squared 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 1 half end cell end table table attributes columnalign right center left columnspacing 0px end attributes row blank blank pi end table table attributes columnalign right center left columnspacing 0px end attributes row blank blank cell left parenthesis 1 half R right parenthesis end cell end table table attributes columnalign right center left columnspacing 0px end attributes row blank blank cell blank squared 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 1 over 8 end cell end table table attributes columnalign right center left columnspacing 0px end attributes row blank blank pi end table table attributes columnalign right center left columnspacing 0px end attributes row blank blank R end table table attributes columnalign right center left columnspacing 0px end attributes row blank blank cell blank squared end cell end table table attributes columnalign right center left columnspacing 0px end attributes row blank blank x end table table attributes columnalign right center left columnspacing 0px end attributes row blank blank cell blank subscript 1 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 over 2 end cell end table table attributes columnalign right center left columnspacing 0px end attributes row blank blank R end table table attributes columnalign right center left columnspacing 0px end attributes row blank blank y end table table attributes columnalign right center left columnspacing 0px end attributes row blank blank cell blank subscript 1 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 fraction numerator 4 r subscript 1 over denominator 3 straight pi end fraction 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 fraction numerator 4 begin display style left parenthesis 1 half R right parenthesis end style over denominator 3 straight pi end fraction 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 fraction numerator 2 R over denominator 3 straight pi end fraction end cell end table end style       

→ Bangun 2

begin mathsize 14px style A subscript 2 equals 1 half pi r subscript 2 squared equals 1 half pi open parentheses R close parentheses squared equals 1 half pi R squared x subscript 2 equals R y subscript 2 equals fraction numerator 4 r subscript 2 over denominator 3 pi end fraction equals fraction numerator 4 open parentheses R close parentheses over denominator 3 pi end fraction equals fraction numerator 4 R over denominator 3 pi end fraction end style 

Titik berat bangun yang diarsir dapat dicari dengan cara

begin mathsize 14px style table attributes columnalign right center left columnspacing 0px end attributes row cell x subscript 0 end cell equals cell fraction numerator x subscript 2 A subscript 2 minus x subscript 1 A subscript 1 over denominator A subscript 2 plus A subscript 1 end fraction end cell row cell x subscript 0 end cell equals cell fraction numerator left parenthesis R right parenthesis left parenthesis 1 half pi R squared right parenthesis minus left parenthesis 3 over 2 R right parenthesis left parenthesis 1 over 8 pi R squared right parenthesis over denominator left parenthesis 1 half pi R squared right parenthesis plus left parenthesis 1 over 8 pi R squared right parenthesis end fraction end cell row cell x subscript 0 end cell equals cell fraction numerator 1 half pi R cubed minus 3 over 16 pi R cubed over denominator 5 over 8 pi R squared end fraction end cell row cell x subscript 0 end cell equals cell fraction numerator 5 over 16 pi R cubed over denominator 5 over 8 pi R squared end fraction end cell row cell x subscript 0 end cell equals cell 1 half R end cell row blank blank blank end table end style   

Sementara itu titik berat pada sumbu y adalah

begin mathsize 14px style table attributes columnalign right center left columnspacing 0px end attributes row cell y subscript 0 end cell equals cell fraction numerator y subscript 2 A subscript 2 minus y subscript 1 A subscript 1 over denominator A subscript 2 plus A subscript 1 end fraction end cell row cell y subscript 0 end cell equals cell fraction numerator left parenthesis fraction numerator 4 R over denominator 3 pi end fraction right parenthesis left parenthesis 1 half pi R squared right parenthesis minus left parenthesis fraction numerator 2 R over denominator 3 pi end fraction right parenthesis left parenthesis 1 over 8 pi R squared right parenthesis over denominator left parenthesis 1 half pi R squared right parenthesis plus left parenthesis 1 over 8 pi R squared right parenthesis end fraction end cell row cell y subscript 0 end cell equals cell fraction numerator 2 over 3 R cubed minus 1 over 12 R cubed over denominator 5 over 8 pi R squared end fraction end cell row cell y subscript 0 end cell equals cell fraction numerator 7 over 12 R cubed over denominator 5 over 8 pi R squared end fraction end cell row cell y subscript 0 end cell equals cell fraction numerator 14 R over denominator 15 pi end fraction end cell row blank blank blank end table end style   

Dengan demikian jawaban yang tepat adalah E.

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