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Jika 3 cos 2 x − sin 2 x = 2 , tunjukkan bahwa cos 2 x = 3 sin 2 x , lalu tentukan semua sudut antara 0 ∘ dan 18 0 ∘ yang memenuhi persamaan trigonometri 3 cos 2 θ − 1 = 1 + sin 2 θ .

Jika , tunjukkan bahwa , lalu tentukan semua sudut antara  dan  yang memenuhi persamaan trigonometri .

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I. Sutiawan

Master Teacher

Mahasiswa/Alumni Universitas Pasundan

Jawaban terverifikasi

Jawaban

sudut antara dan yang memenuhi persamaan trigonometri adalah dan .

 sudut antara 0 degree dan 180 degree yang memenuhi persamaan trigonometri 3 space cos squared theta minus 1 equals 1 plus space sin squared theta adalah 30 degree dan 150 degree.

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Pembahasan

Ingat! Maka: Maka: tidak memenuhi karena berada diantara dan . Jadi,sudut antara dan yang memenuhi persamaan trigonometri adalah dan .

Ingat!

table attributes columnalign right center left columnspacing 0px end attributes row cell sin space x end cell equals cell sin space alpha end cell row x equals cell alpha plus k.360 degree end cell row blank blank atau row x equals cell left parenthesis 180 minus alpha right parenthesis plus k.360 degree end cell end table 

table attributes columnalign right center left columnspacing 0px end attributes row cell sin squared x plus cos squared x end cell equals 1 row blank rightwards double arrow cell cos squared x equals 1 minus sin squared x end cell end table 

Maka:

begin mathsize 12px style table attributes columnalign right center left columnspacing 0px end attributes row cell 3 space cos squared x minus sin squared x end cell equals 2 row cell 3 space cos squared x minus sin squared x minus 2 end cell equals 0 row cell 3 space cos squared x minus sin squared x minus 2 left parenthesis 1 right parenthesis end cell equals 0 row cell 3 space cos squared x minus sin squared x minus 2 left parenthesis sin squared x plus cos squared x right parenthesis end cell equals 0 row cell 3 space cos squared x minus sin squared x minus 2 space sin squared x minus 2 space cos squared x end cell equals 0 row cell cos squared x minus 3 space sin squared x end cell equals 0 row cell cos squared x end cell equals cell 3 space sin squared x end cell row blank blank cell left parenthesis terbukti right parenthesis end cell end table end style  

Maka:

begin mathsize 12px style table attributes columnalign right center left columnspacing 0px end attributes row cell 3 space cos squared theta minus 1 end cell equals cell 1 plus space sin squared theta end cell row cell 3 space cos squared theta minus 1 minus 1 minus sin squared theta end cell equals 0 row cell 3 space cos squared theta minus sin squared theta minus 2 end cell equals 0 row cell 3 left parenthesis 1 minus sin squared theta right parenthesis minus sin squared theta minus 2 end cell equals 0 row cell 3 minus 3 space sin squared minus sin squared theta minus 2 end cell equals 0 row cell negative 4 space sin squared theta plus 1 end cell equals 0 row cell 4 space sin squared theta minus 1 end cell equals 0 row cell left parenthesis 2 space sin space theta plus 1 right parenthesis left parenthesis 2 space sin space theta right parenthesis end cell equals 0 end table end style  

begin mathsize 12px style sin space theta equals negative 1 half space atau space sin space theta equals 1 half end style  

  • sin space theta equals negative 1 half  

sin space theta equals negative 1 half sin space theta equals sin space 210 degree 

tidak memenuhi karena theta berada diantara 0 degree dan 180 degree.

  • sin space theta equals 1 half 

table attributes columnalign right center left columnspacing 0px end attributes row cell sin space theta end cell equals cell 1 half end cell row cell sin space theta end cell equals cell sin space 30 degree end cell row theta equals cell 30 degree plus k.360 degree end cell row blank blank blank row k equals 0 row blank rightwards double arrow cell theta equals 30 degree plus 0.360 degree end cell row blank blank blank row theta equals cell left parenthesis 180 degree minus 30 degree right parenthesis plus k.360 degree end cell row blank equals cell 150 degree plus k.360 degree end cell row blank blank blank row k equals 0 row blank rightwards double arrow cell theta equals 150 degree plus 0.360 degree end cell row blank equals cell 150 degree end cell end table 

Jadi, sudut antara 0 degree dan 180 degree yang memenuhi persamaan trigonometri 3 space cos squared theta minus 1 equals 1 plus space sin squared theta adalah 30 degree dan 150 degree.

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