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Tentukan semua nilai θ , untuk 0 ∘ ≤ θ ≤ 18 0 ∘ yang memenuhi, 8 cos 4 θ + 1 = 8 cos 2 θ + 2 1 ​ 3 ​ . Buktikan bahwa: 2 ( sin 6 θ + cos 6 θ ) − 3 ( sin 4 θ + cos 4 θ ) = − 1 .

Tentukan semua nilai , untuk  yang memenuhi, .
Buktikan bahwa: .

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I. Sutiawan

Master Teacher

Mahasiswa/Alumni Universitas Pasundan

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pembuktian bahwa persamaan adalah benar adalah uraian yang telah dipaparkan di atas.

pembuktian bahwa persamaan 2 left parenthesis sin to the power of 6 theta plus cos to the power of 6 theta right parenthesis minus 3 left parenthesis sin to the power of 4 theta plus cos to the power of 4 theta right parenthesis equals negative 1 adalah benar adalah uraian yang telah dipaparkan di atas.

Pembahasan

Diketahui . untuk . Ingat! Misalkan , maka: Dengan menggunakan rumus kuadratik persamaan kuadrat, maka: atau Jadi, nilai yang memenuhi untuk adalah . Akan kita buktikan . Ingat! Maka: Jadi, pembuktian bahwa persamaan adalah benar adalah uraian yang telah dipaparkan di atas.

Diketahui 8 space cos to the power of 4 theta plus 1 equals 8 space cos squared theta plus 1 half square root of 3. untuk 0 degree less or equal than theta less or equal than 180 degree.

Ingat!

  • table attributes columnalign right center left columnspacing 0px end attributes row cell cos space x end cell equals cell cos space alpha end cell row x equals cell alpha plus k.360 degree end cell row blank blank atau row x equals cell negative alpha plus k.360 degree end cell end table 

Misalkan cos squared theta equals x, maka:

table attributes columnalign right center left columnspacing 0px end attributes row cell 8 space cos to the power of 4 theta plus 1 end cell equals cell 8 space cos squared theta plus 1 half square root of 3 end cell row cell 8 x squared plus 1 end cell equals cell 8 x plus 1 half square root of 3 end cell row blank blank blank end table 
Error converting from MathML to accessible text. 

Dengan menggunakan rumus kuadratik persamaan kuadrat, maka:

table attributes columnalign right center left columnspacing 0px end attributes row x equals cell fraction numerator negative left parenthesis negative 8 right parenthesis plus-or-minus square root of left parenthesis negative 8 right parenthesis squared minus 4 left parenthesis 8 right parenthesis left parenthesis 1 minus begin display style 1 half end style square root of 3 right parenthesis end root over denominator 2 left parenthesis 8 right parenthesis end fraction end cell row blank equals cell fraction numerator 8 plus-or-minus square root of 64 minus 32 plus 16 square root of 3 end root over denominator 16 end fraction end cell row blank equals cell fraction numerator 8 plus-or-minus square root of 32 plus 16 square root of 3 end root over denominator 16 end fraction end cell row blank blank blank row cell cos squared theta end cell equals cell fraction numerator 8 plus-or-minus square root of 32 plus 16 square root of 3 end root over denominator 16 end fraction end cell row cell cos space theta end cell equals cell plus-or-minus open parentheses fraction numerator 8 plus-or-minus square root of 32 plus 16 square root of 3 end root over denominator 16 end fraction close parentheses end cell row cell cos space theta end cell equals cell open parentheses fraction numerator 8 plus-or-minus square root of 32 plus 16 square root of 3 end root over denominator 16 end fraction close parentheses end cell end table 

table attributes columnalign right center left columnspacing 0px end attributes row blank blank cos 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 theta 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 open parentheses fraction numerator 8 plus square root of 32 plus 16 square root of 3 end root over denominator 16 end fraction close parentheses end cell end table atau table attributes columnalign right center left columnspacing 0px end attributes row blank blank cos 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 theta 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 open parentheses fraction numerator 8 minus square root of 32 plus 16 square root of 3 end root over denominator 16 end fraction close parentheses end cell end table 

table attributes columnalign right center left columnspacing 0px end attributes row cell cos space theta end cell equals cell open parentheses fraction numerator 8 plus square root of 32 plus 16 square root of 3 end root over denominator 16 end fraction close parentheses end cell row cell cos space theta end cell equals cell cos space 7 comma 5 degree end cell row theta equals cell 7 comma 5 degree plus k.360 degree end cell row blank blank blank row k equals 0 row blank rightwards double arrow cell theta equals 7 comma 5 degree plus 0.360 degree end cell row blank equals cell 7 comma 5 degree end cell end table 

table attributes columnalign right center left columnspacing 0px end attributes row cell cos space theta end cell equals cell open parentheses fraction numerator 8 minus square root of 32 plus 16 square root of 3 end root over denominator 16 end fraction close parentheses end cell row cell cos space theta end cell equals cell cos space 82 comma 5 degree end cell row theta equals cell 82 comma 5 degree plus k.360 degree end cell row blank blank blank row k equals 0 row blank rightwards double arrow cell theta equals 82 comma 5 degree plus 0.360 degree end cell row blank equals cell 82 comma 5 degree end cell end table  

Jadi, nilai theta yang memenuhi 8 space cos to the power of 4 theta plus 1 equals 8 space cos squared theta plus 1 half square root of 3 untuk 0 degree less or equal than theta less or equal than 180 degree adalah 7 comma 5 degree space atau space 82 comma 5 degree

 

Akan kita buktikan 2 left parenthesis sin to the power of 6 theta plus cos to the power of 6 theta right parenthesis minus 3 left parenthesis sin to the power of 4 theta plus cos to the power of 4 theta right parenthesis equals negative 1.

Ingat!

  • sin squared theta plus cos squared theta equals 1
  • a squared plus b squared equals left parenthesis a plus b right parenthesis squared minus 2 a b
  • a cubed plus b cubed equals left parenthesis a plus b right parenthesis left parenthesis a squared minus a b plus b squared right parenthesis 

Maka:

begin mathsize 12px style 2 left parenthesis sin to the power of 6 theta plus cos to the power of 6 theta right parenthesis minus 3 left parenthesis sin to the power of 4 theta plus cos to the power of 4 theta right parenthesis equals negative 1 2 open parentheses open parentheses sin squared theta close parentheses cubed plus open parentheses cos to the power of 6 theta close parentheses cubed close parentheses minus 3 open parentheses open parentheses sin squared theta close parentheses squared plus open parentheses cos squared theta close parentheses squared close parentheses equals negative 1 2 open parentheses sin squared theta plus cos squared theta close parentheses open parentheses sin to the power of 4 theta minus sin squared theta. cos squared theta plus cos to the power of 4 theta close parentheses minus 3 open parentheses sin squared theta plus cos squared theta close parentheses squared minus 2. sin squared theta. cos squared theta right parenthesis equals negative 1 2 left parenthesis 1 right parenthesis open parentheses sin to the power of 4 theta minus sin squared theta. cos squared theta plus cos to the power of 4 theta close parentheses minus 3 left parenthesis 1 minus 2. sin squared theta. cos squared theta right parenthesis equals negative 1 2 space sin to the power of 4 theta minus 2 space sin squared theta. cos squared theta plus 2 space cos to the power of 4 theta minus 3 plus 6 space sin squared theta. cos squared theta equals negative 1 2 space sin to the power of 4 theta plus 2 space cos to the power of 4 theta plus 4 space sin squared theta. cos squared theta minus 3 equals negative 1 2 open parentheses open parentheses sin squared theta close parentheses squared plus open parentheses cos squared theta close parentheses squared close parentheses plus 4 space sin squared theta. cos squared theta minus 3 equals negative 1 2 open parentheses 1 minus 2 sin squared theta. cos squared theta close parentheses plus 4 space sin squared theta. cos squared theta minus 3 equals negative 1 2 minus 4 space sin squared theta. cos squared theta plus 4 space sin squared theta. cos squared theta minus 3 equals negative 1 2 minus 3 equals negative 1 minus 1 equals negative 1 left parenthesis terbukti right parenthesis end style 

Jadi, pembuktian bahwa persamaan 2 left parenthesis sin to the power of 6 theta plus cos to the power of 6 theta right parenthesis minus 3 left parenthesis sin to the power of 4 theta plus cos to the power of 4 theta right parenthesis equals negative 1 adalah benar adalah uraian yang telah dipaparkan di atas.

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