Roboguru

Diketahui . Invers dari  adalah .

Pertanyaan

Diketahui f open parentheses x close parentheses equals 5 x minus 4. Invers dari f open parentheses x close parentheses adalah f to the power of negative 1 end exponent open parentheses x close parentheses equals....

  1. x minus 4  

  2. x plus 4  

  3. fraction numerator x plus 4 over denominator 5 end fraction  

  4. 5 x minus 20 

  5. 5 x plus 20  

Pembahasan Soal:

Invers fungsi linear.

Diketahui:
f open parentheses x close parentheses equals 5 x minus 4. Akan ditentukan f to the power of negative 1 end exponent open parentheses x close parentheses.

Perhatikan perhitungan berikut.

table attributes columnalign right center left columnspacing 2px end attributes row cell f open parentheses x close parentheses end cell equals cell 5 x minus 4 end cell row y equals cell 5 x minus 4 end cell row cell y plus 4 end cell equals cell 5 x end cell row cell 5 x end cell equals cell y plus 4 end cell row x equals cell fraction numerator y plus 4 over denominator 5 end fraction end cell row cell f to the power of negative 1 end exponent open parentheses x close parentheses end cell equals cell fraction numerator x plus 4 over denominator 5 end fraction end cell end table

Jadi, jawaban yang tepat adalah C.

Pembahasan terverifikasi oleh Roboguru

Dijawab oleh:

N. Dwi

Mahasiswa/Alumni Universitas Negeri Yogyakarta

Terakhir diupdate 02 Mei 2021

Roboguru sudah bisa jawab 91.4% pertanyaan dengan benar

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Pertanyaan yang serupa

Diketahui  dan . Apakah ?  Sifat apa yang dapat kalian temukan dari fungsi invers pada komposisi?

Pembahasan Soal:

  • Untuk mengecek persamaan tersebut, kita cari fungsi masing-masing untuk ruas kanan dan ruas kiri.

Pada ruas kanan, invers dari fungsi linear f left parenthesis x right parenthesis dan g left parenthesis x right parenthesis adalah:

table attributes columnalign right center left columnspacing 0px end attributes row cell f left parenthesis x right parenthesis end cell equals cell x plus 2 end cell row x equals cell f left parenthesis x right parenthesis minus 2 end cell row cell f to the power of negative 1 end exponent left parenthesis x right parenthesis end cell equals cell x minus 2 end cell end table 

table attributes columnalign right center left columnspacing 0px end attributes row cell g left parenthesis x right parenthesis end cell equals cell 3 x minus 10 end cell row cell 3 x end cell equals cell g left parenthesis x right parenthesis plus 10 end cell row x equals cell fraction numerator g left parenthesis x right parenthesis plus 10 over denominator 3 end fraction end cell row cell g to the power of negative 1 end exponent left parenthesis x right parenthesis end cell equals cell fraction numerator x plus 10 over denominator 3 end fraction end cell end table  

Sehingga,

 table attributes columnalign right center left columnspacing 0px end attributes row cell left parenthesis f to the power of negative 1 end exponent ring operator g to the power of negative 1 end exponent right parenthesis left parenthesis x right parenthesis end cell equals cell f to the power of negative 1 end exponent left parenthesis g to the power of negative 1 end exponent left parenthesis x right parenthesis right parenthesis end cell row blank equals cell f to the power of negative 1 end exponent open parentheses fraction numerator x plus 10 over denominator 3 end fraction close parentheses end cell row blank equals cell open parentheses fraction numerator x plus 10 over denominator 3 end fraction close parentheses minus 2 end cell row blank equals cell fraction numerator x plus 10 minus 6 over denominator 3 end fraction end cell row blank equals cell fraction numerator x plus 4 over denominator 3 end fraction end cell end table

Untuk invers fungsi komposisi pada ruas kiri:

table attributes columnalign right center left columnspacing 0px end attributes row cell open parentheses g ring operator f close parentheses left parenthesis x right parenthesis end cell equals cell g left parenthesis f left parenthesis x right parenthesis right parenthesis end cell row cell open parentheses g ring operator f close parentheses left parenthesis x right parenthesis end cell equals cell g left parenthesis x plus 2 right parenthesis end cell row cell open parentheses g ring operator f close parentheses left parenthesis x right parenthesis end cell equals cell 3 left parenthesis x plus 2 right parenthesis minus 10 end cell row cell open parentheses g ring operator f close parentheses left parenthesis x right parenthesis end cell equals cell 3 x plus 6 minus 10 end cell row cell open parentheses g ring operator f close parentheses left parenthesis x right parenthesis end cell equals cell 3 x minus 4 end cell row cell 3 x end cell equals cell open parentheses g ring operator f close parentheses left parenthesis x right parenthesis plus 4 end cell row x equals cell fraction numerator open parentheses g ring operator f close parentheses left parenthesis x right parenthesis plus 4 over denominator 3 end fraction end cell row cell open parentheses g ring operator f close parentheses to the power of negative 1 end exponent left parenthesis x right parenthesis end cell equals cell fraction numerator x plus 4 over denominator 3 end fraction end cell end table 

Karena ruas kanan dan ruas kiri masing-masing menghasilkan fungsi yang sama yaitu fraction numerator x plus 4 over denominator 3 end fraction, maka left parenthesis f to the power of negative 1 end exponent ring operator g to the power of negative 1 end exponent right parenthesis left parenthesis x right parenthesis equals open parentheses g ring operator f close parentheses to the power of negative 1 end exponent left parenthesis x right parenthesis.

Dengan demikian, benar bahwa left parenthesis f to the power of negative 1 end exponent ring operator g to the power of negative 1 end exponent right parenthesis left parenthesis x right parenthesis equals open parentheses g ring operator f close parentheses to the power of negative 1 end exponent left parenthesis x right parenthesis.

  • Sifat yang dapat ditemukan dari fungsi invers pada komposisi adalah invers dari suatu fungsi komposisi left parenthesis f ring operator g right parenthesis to the power of negative 1 end exponent left parenthesis x right parenthesis sama dengan menginverskan masing-masing fungsi kemudian mengkomposisikannya secara terbalik sebagai mana persamaan open parentheses f ring operator g close parentheses to the power of negative 1 end exponent left parenthesis x right parenthesis equals left parenthesis g to the power of negative 1 end exponent ring operator f to the power of negative 1 end exponent right parenthesis left parenthesis x right parenthesis.

Dengan demikian, sifat fungsi invers pada komposisi yang dapat ditemukan adalah open parentheses f ring operator g close parentheses to the power of negative 1 end exponent left parenthesis x right parenthesis equals left parenthesis g to the power of negative 1 end exponent ring operator f to the power of negative 1 end exponent right parenthesis left parenthesis x right parenthesis.

Roboguru

Diketahui  dan . Jika  adalah invers dari  maka nilai dari

Pembahasan Soal:

Diketahui f left parenthesis x right parenthesis equals 2 x minus 3 dan open parentheses f ring operator g close parentheses left parenthesis x right parenthesis equals 4 x minus 9.  Maka:

table attributes columnalign right center left columnspacing 0px end attributes row cell open parentheses f ring operator g close parentheses left parenthesis x right parenthesis end cell equals cell f left parenthesis g left parenthesis x right parenthesis right parenthesis end cell row cell 4 x minus 9 end cell equals cell 2 g left parenthesis x right parenthesis minus 3 end cell row cell 2 g left parenthesis x right parenthesis end cell equals cell 4 x minus 9 plus 3 end cell row cell 2 g left parenthesis x right parenthesis end cell equals cell 4 x minus 6 end cell row cell g left parenthesis x right parenthesis end cell equals cell fraction numerator 4 x minus 6 over denominator 2 end fraction end cell row cell g left parenthesis x right parenthesis end cell equals cell 2 x minus 3 end cell end table

Sehingga: 

table attributes columnalign right center left columnspacing 0px end attributes row cell g left parenthesis x right parenthesis end cell equals cell 2 x minus 3 end cell row y equals cell 2 x minus 3 end cell row cell 2 x end cell equals cell y plus 3 end cell row x equals cell fraction numerator y plus 3 over denominator 2 end fraction end cell row cell g to the power of negative 1 end exponent left parenthesis x right parenthesis end cell equals cell fraction numerator x plus 3 over denominator 2 end fraction end cell row cell g to the power of negative 1 end exponent left parenthesis 3 right parenthesis end cell equals cell fraction numerator 3 plus 3 over denominator 2 end fraction end cell row blank equals cell 6 over 2 end cell row blank equals 3 end table

Jadi, jawaban yang tepat adaah B

Roboguru

Diketahui  dan   b.  ?

Pembahasan Soal:

Dengan menggunakan rumus invers fungsi

begin mathsize 14px style z open parentheses x close parentheses equals a x plus b blank semicolon a not equal to 0 z to the power of negative 1 end exponent open parentheses x close parentheses equals fraction numerator x minus b over denominator a end fraction blank semicolon a not equal to 0 end style 

Diperoleh 

begin mathsize 14px style f open parentheses x close parentheses equals x minus 3 f to the power of negative 1 end exponent open parentheses x close parentheses equals x plus 3 g open parentheses x close parentheses equals 2 x plus 4 g to the power of negative 1 end exponent open parentheses x close parentheses equals fraction numerator x minus 4 over denominator 2 end fraction end style  

Nilai begin mathsize 14px style left parenthesis g to the power of negative 1 end exponent ring operator f to the power of negative 1 end exponent right parenthesis left parenthesis x right parenthesis end style adalah begin mathsize 14px style f to the power of negative 1 end exponent end style dimasukkan ke begin mathsize 14px style g to the power of negative 1 end exponent space colon space left parenthesis g to the power of negative 1 end exponent ring operator f to the power of negative 1 end exponent right parenthesis left parenthesis x right parenthesis equals g to the power of negative 1 end exponent left parenthesis f to the power of negative 1 end exponent left parenthesis x right parenthesis right parenthesis end style 

begin mathsize 14px style left parenthesis g to the power of negative 1 end exponent ring operator f to the power of negative 1 end exponent right parenthesis left parenthesis x right parenthesis equals fraction numerator left parenthesis x plus 3 right parenthesis minus 4 over denominator 2 end fraction left parenthesis g to the power of negative 1 end exponent ring operator f to the power of negative 1 end exponent right parenthesis left parenthesis x right parenthesis equals fraction numerator x minus 1 over denominator 2 end fraction end style  

Jadi, diperoleh bahwa begin mathsize 14px style left parenthesis g to the power of negative 1 end exponent ring operator f to the power of negative 1 end exponent right parenthesis left parenthesis x right parenthesis equals fraction numerator x minus 1 over denominator 2 end fraction end style                undefined 

Roboguru

Fungsi  dan  didefinisakan oleh  dan , Tentukan: c.

Pembahasan Soal:

Menentukan begin mathsize 14px style f to the power of negative 1 end exponent open parentheses x close parentheses end style

  undefined 

Menentukan begin mathsize 14px style left parenthesis g ring operator f to the power of negative 1 end exponent right parenthesis left parenthesis x right parenthesis end style   

begin mathsize 14px style table attributes columnalign right center left columnspacing 0px end attributes row cell open parentheses g ring operator f to the power of negative 1 end exponent close parentheses open parentheses x close parentheses end cell equals cell g open parentheses f to the power of negative 1 end exponent open parentheses x close parentheses close parentheses end cell row blank equals cell g open parentheses fraction numerator x minus 11 over denominator 2 end fraction close parentheses end cell row blank equals cell 1 minus open parentheses fraction numerator x minus 11 over denominator 2 end fraction close parentheses end cell row blank equals cell 2 over 2 minus x over 2 plus 11 over 2 end cell row blank equals cell 13 over 2 minus x over 2 end cell row blank equals cell fraction numerator 13 minus x over denominator 2 end fraction end cell end table end style 

Roboguru

Diketahui fungsi  dan . Jika , maka nilai  adalah ...

Pembahasan Soal:

Tentukan invers fungsinya terlebih dahulu.

table attributes columnalign right center left columnspacing 0px end attributes row cell f open parentheses x close parentheses end cell equals cell x cubed end cell row y equals cell x cubed end cell row x equals cell cube root of y end cell row cell f to the power of negative 1 end exponent open parentheses x close parentheses end cell equals cell cube root of x end cell row blank blank blank row cell g open parentheses x close parentheses end cell equals cell 3 x minus 4 end cell row y equals cell 3 x minus 4 end cell row x equals cell fraction numerator y plus 4 over denominator 3 end fraction end cell row cell g to the power of negative 1 end exponent open parentheses x close parentheses end cell equals cell fraction numerator x plus 4 over denominator 3 end fraction end cell end table

Kemudian dari fungsi-fungsi invers tersebut gunakan rumus fungsi komposisi untuk mengetahui nilai a.

table attributes columnalign right center left columnspacing 0px end attributes row cell open parentheses g to the power of negative 1 end exponent ring operator f to the power of negative 1 end exponent close parentheses open parentheses 8 close parentheses end cell equals a row cell g to the power of negative 1 end exponent open parentheses f to the power of negative 1 end exponent open parentheses 8 close parentheses close parentheses end cell equals a row cell g to the power of negative 1 end exponent open parentheses cube root of 8 close parentheses end cell equals a row cell fraction numerator cube root of 8 plus 4 over denominator 3 end fraction end cell equals a row cell fraction numerator 2 plus 4 over denominator 3 end fraction end cell equals a row cell 6 over 3 end cell equals a row 2 equals a end table

Kemudian diperoleh:

table attributes columnalign right center left columnspacing 0px end attributes row cell open parentheses f to the power of negative 1 end exponent ring operator g to the power of negative 1 end exponent close parentheses open parentheses 10 a close parentheses end cell equals cell f to the power of negative 1 end exponent open parentheses g to the power of negative 1 end exponent open parentheses 10 open parentheses 2 close parentheses close parentheses close parentheses end cell row blank equals cell f to the power of negative 1 end exponent open parentheses g to the power of negative 1 end exponent open parentheses 20 close parentheses close parentheses end cell row blank equals cell f to the power of negative 1 end exponent open parentheses fraction numerator 20 plus 4 over denominator 3 end fraction close parentheses end cell row blank equals cell cube root of fraction numerator 20 plus 4 over denominator 3 end fraction end root end cell row blank equals cell cube root of 24 over 3 end root end cell row blank equals cell cube root of 8 end cell row blank equals 2 end table

Maka, nilai open parentheses f to the power of negative 1 end exponent ring operator g to the power of negative 1 end exponent close parentheses open parentheses 10 a close parentheses adalah 2.

Roboguru

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