Roboguru

Diketahui segiiga ABC dengan panjang sisi-sisinya AB = 9 cm, AC = 8 cm, dan BC = 7 cm. Tentukan nilai  dan .

Pertanyaan

Diketahui segiiga ABC dengan panjang sisi-sisinya AB = 9 cm, AC = 8 cm, dan BC = 7 cm. Tentukan nilai sin A dan tan A.

Pembahasan Soal:

kita bisa menggunakan aturan cosinus,  

cos A equals fraction numerator A B squared plus A C squared minus B C squared over denominator 2. A B. A C end fraction space space space space space space space space equals fraction numerator 9 squared plus 8 squared minus 7 squared over denominator 2.9.8 end fraction space space space space space space space space equals fraction numerator 81 plus 64 minus 49 over denominator 144 end fraction space space space space space space space space equals 96 over 144 space space space space space space space space equals 2 over 3

Kemudian, gambar segitiga siku-siku ABC, misal siku-siku di B. 

kita tahu bahwa cosinus adalah samping per miring. jadi, AB = 2, AC = 3, 

B C equals square root of A C squared minus A B squared end root space space space space space equals square root of 3 squared minus 2 squared end root space space space space space equals square root of 9 minus 4 end root space space space space space equals square root of 5 

maka kita bisa mencari sinA dan tanA dari segitiga siku-siku ABC tersebut.

sin A equals fraction numerator B C over denominator A C end fraction space space space space space space space space space space space space space space space space space space space space tan A equals fraction numerator B C over denominator A B end fraction space space space space space space space space space equals fraction numerator square root of 5 over denominator 3 end fraction space space space space space space space space space space space space space space space space space space space space space space space space space space space space space equals fraction numerator square root of 5 over denominator 2 end fraction

Jadi, sin A equals 1 third square root of 5 comma space dan tan A equals 1 half square root of 5

Pembahasan terverifikasi oleh Roboguru

Dijawab oleh:

L. Marlina

Mahasiswa/Alumni Institut Teknologi Bandung

Terakhir diupdate 30 April 2021

Roboguru sudah bisa jawab 91.4% pertanyaan dengan benar

Tapi Roboguru masih mau belajar. Menurut kamu pembahasan kali ini sudah membantu, belum?

Membantu

Kurang Membantu

Apakah pembahasan ini membantu?

Belum menemukan yang kamu cari?

Post pertanyaanmu ke Tanya Jawab, yuk

Mau Bertanya

Pertanyaan yang serupa

Pada suat segitiga PQR, diketahui,  serta . Jika , maka nilai dari  adalah ....

Pembahasan Soal:

Ingat bahwa, pada aturan cosinus berlaku c squared equals a squared plus b squared minus 2 a b cos angle c, sehingga

table attributes columnalign right center left columnspacing 0px end attributes row cell R Q squared end cell equals cell P Q squared plus P R squared minus 2 P Q times P R space cos space angle P end cell row cell open parentheses 3 square root of 3 close parentheses squared end cell equals cell open parentheses 2 square root of 5 close parentheses squared plus P R squared minus 2 cross times 2 square root of 5 cross times P R cross times cos space 60 degree end cell row 27 equals cell 20 plus P R squared minus 4 square root of 5 P R cross times 1 half end cell row 7 equals cell P R squared minus 2 square root of 5 P R end cell row cell Misal colon x end cell equals cell P R comma space maka end cell row cell straight x squared minus 2 square root of 5 straight x minus 7 end cell equals 0 row cell straight x subscript 1 comma 2 end subscript end cell equals cell fraction numerator negative straight b plus-or-minus square root of straight b squared minus 4 ac end root over denominator 2 straight a end fraction end cell row blank equals cell fraction numerator 2 square root of 5 plus-or-minus square root of 20 plus 28 end root over denominator 2 end fraction end cell row blank equals cell square root of 5 plus-or-minus 2 square root of 3 end cell row blank rightwards arrow cell PR equals square root of 5 plus 2 square root of 3 end cell end table

Melalui aturan cosinus, diperoleh

table attributes columnalign right center left columnspacing 0px end attributes row cell cos space angle R end cell equals cell fraction numerator R Q squared plus R P squared minus P Q squared over denominator 2 R Q times R P end fraction end cell row blank equals cell fraction numerator 27 plus open parentheses square root of 5 plus 2 square root of 3 close parentheses squared minus 20 over denominator 2 open parentheses 3 square root of 3 close parentheses open parentheses square root of 5 plus 2 square root of 3 close parentheses end fraction end cell row blank equals cell fraction numerator 7 plus 5 plus 12 plus 4 square root of 15 over denominator 6 square root of 15 plus 36 end fraction end cell row blank equals cell fraction numerator 24 plus 4 square root of 15 over denominator 36 plus 6 square root of 15 end fraction end cell row blank equals cell fraction numerator 4 left parenthesis 6 plus square root of 15 right parenthesis over denominator 6 left parenthesis 6 plus square root of 15 right parenthesis end fraction end cell row blank equals cell 2 over 3 end cell row blank rightwards arrow cell m plus n equals 2 plus 3 end cell row blank equals 5 end table

Oleh karena itu, nilai dari table attributes columnalign right center left columnspacing 0px end attributes row cell m plus n end cell equals 5 end table.

Roboguru

Kapal P dan Q berlayar dari A pada waktu yang sama. P berlayar dengan jurusan tiga angka dengan kecepatan rata-rata . Kapal Q berlayar dengan jurusan tiga angka dengan kecepatan rata-rata . Jarak kedu...

Pembahasan Soal:

  • Menentukan jarak P ke A. 

table attributes columnalign right center left columnspacing 0px end attributes row cell S subscript P A end subscript end cell equals cell V subscript p cross times t end cell row blank equals cell 8 space mil divided by jam cross times 2 space jam end cell row blank equals cell 16 space mil end cell end table

  • Menentukan jarak Q ke A

table attributes columnalign right center left columnspacing 0px end attributes row cell S subscript Q A end subscript end cell equals cell V subscript Q cross times t end cell row blank equals cell 14 space mil divided by jam cross times 2 space jam end cell row blank equals cell 28 space mil end cell end table

  • Menentukan sudut A.

table attributes columnalign right center left columnspacing 0px end attributes row cell Sudut space straight A end cell equals cell Sudut space straight Q minus Sudut space straight P end cell row blank equals cell 90 degree minus 30 degree end cell row blank equals cell 60 degree end cell end table

  • Menentukan jarak kapal P da Q ( menggunakan aturan cosinus)

table attributes columnalign right center left columnspacing 0px end attributes row cell P Q squared end cell equals cell S subscript P A end subscript squared plus S subscript Q A end subscript squared minus 2 open parentheses S subscript P A end subscript close parentheses open parentheses S subscript Q A end subscript close parentheses cos space 60 degree end cell row cell P Q squared end cell equals cell 16 squared plus 28 squared minus 2 open parentheses 16 close parentheses open parentheses 28 close parentheses 1 half end cell row cell P Q squared end cell equals cell 256 plus 784 minus 448 end cell row cell P Q squared end cell equals 592 row cell P Q end cell equals cell square root of 592 end cell row cell P Q end cell equals cell 4 square root of 37 end cell end table

Jadi, jarak kedua kapal P dan Q berlayar selama 2 jam adalah 4 square root of 37 mil

Roboguru

Rio akan mengukur tinggi pohon menggunakan bantuan klinometer. Rio melihat ujung pohon dari jarak tertentu dengan sudut elevasi . Rio berjalan mendekati pohon sejauh  dari tempat semula. Pada saat itu...

Pembahasan Soal:

Roboguru

Perhatikan gambar berikut.    Gambar tersebut menunjukkan . Jika  adalah garis berat dari titik sudut C, buktikanlah:   Petunjuk: Gunakan aturan kosinus dalam

Pembahasan Soal:

Roboguru

Diketahui segitiga ABC dengan panjang , , dan . Nilai sinus sudut  adalah . . . .

Pembahasan Soal:

Gambar segitiga:

Menghitung nilai cos pada sudut A dengan menggunakan aturan cosinus:

begin mathsize 14px style 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 straight A 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 AC squared plus AB squared minus BC squared over denominator 2 times AC times AB end fraction 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 straight A 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 12 squared plus 3 squared minus left parenthesis 6 square root of 3 right parenthesis squared over denominator 2 times 12 times 3 end fraction 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 straight A 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 144 plus 9 minus 108 over denominator 72 end fraction 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 straight A 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 45 over 72 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 straight A 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 cell 5 over 8 end cell equals cell AO over AB end cell end table end style

Menghitung panjang sisi segitiga siku-siku:
a) Panjang AO:

begin mathsize 14px style table attributes columnalign right center left columnspacing 0px end attributes row AO equals cell 5 over 8 cross times AB end cell row blank equals cell 5 over 8 cross times 3 space text cm end text end cell row blank equals cell 15 over 8 space text cm end text end cell end table end style

b) Panjang BO:

begin mathsize 14px style table attributes columnalign right center left columnspacing 0px end attributes row BO equals cell square root of 3 squared minus left parenthesis 15 over 8 right parenthesis squared end root end cell row BO equals cell square root of 9 minus 225 over 64 end root end cell row BO equals cell square root of fraction numerator 576 minus 225 over denominator 64 end fraction end root end cell row BO equals cell square root of 351 over 64 end root end cell row BO equals cell square root of fraction numerator 9 cross times 39 over denominator 64 end fraction end root end cell row BO equals cell 3 over 8 square root of 39 space text cm end text end cell end table end style

Menghitung nilai sin A:

begin mathsize 14px style sin space straight A equals BO over AB sin space straight A equals fraction numerator begin display style 3 over 8 square root of 39 end style over denominator 3 end fraction sin space straight A equals 1 over 8 square root of 39 end style

Jadi, jawaban yang tepat adalah C.

Roboguru

Roboguru sudah bisa jawab 91.4% pertanyaan dengan benar

Tapi Roboguru masih mau belajar. Menurut kamu pembahasan kali ini sudah membantu, belum?

Membantu

Kurang Membantu

Apakah pembahasan ini membantu?

Belum menemukan yang kamu cari?

Post pertanyaanmu ke Tanya Jawab, yuk

Mau Bertanya

RUANGGURU HQ

Jl. Dr. Saharjo No.161, Manggarai Selatan, Tebet, Kota Jakarta Selatan, Daerah Khusus Ibukota Jakarta 12860

Coba GRATIS Aplikasi Ruangguru

Produk Ruangguru

Produk Lainnya

Hubungi Kami

Ikuti Kami

©2021 Ruangguru. All Rights Reserved