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Tentukan rumus dari f + g , f − g , g − f dan f × g untuk f dan g pada R dengan ketentuan sebagai berikut: b. f ( x ) = x + 1 1 ​ , untuk x  = − 1 dan ( x ) = 2 x − 4 5 x ​ , untuk x  = 2

Tentukan rumus dari , ,  dan  untuk  dan  pada  dengan ketentuan sebagai berikut:

b. , untuk  dan , untuk  

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N. Indah

Master Teacher

Mahasiswa/Alumni Universitas Diponegoro

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Jawaban

diperoleh rumusnya adalah ( f + g ) ( x ) = 2 x 2 − 2 x − 4 5 x 2 + 7 x − 4 ​ , ( f − g ) ( x ) = 2 x 2 − 2 x − 4 − 5 x 2 − 3 x − 4 ​ , ( g − f ) ( x ) = 2 x 2 − 2 x − 4 5 x 2 + 3 x + 4 ​ , dan ( f × g ) ( x ) = 2 x 2 − 4 x + 2 x − 4 5 x ​ .

diperoleh rumusnya adalah , dan .

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Pembahasan

Diketahui , untuk dan g ( x ) = 2 x − 4 5 x ​ , untuk , maka: Dengan demikian, diperoleh rumusnya adalah ( f + g ) ( x ) = 2 x 2 − 2 x − 4 5 x 2 + 7 x − 4 ​ , ( f − g ) ( x ) = 2 x 2 − 2 x − 4 − 5 x 2 − 3 x − 4 ​ , ( g − f ) ( x ) = 2 x 2 − 2 x − 4 5 x 2 + 3 x + 4 ​ , dan ( f × g ) ( x ) = 2 x 2 − 4 x + 2 x − 4 5 x ​ .

Diketahui  begin mathsize 14px style f left parenthesis x right parenthesis equals fraction numerator 1 over denominator x plus 1 end fraction end style, untuk begin mathsize 14px style x not equal to negative 1 end style dan , untuk begin mathsize 14px style x not equal to 2 end style, maka:

begin mathsize 14px style table attributes columnalign right center left columnspacing 0px end attributes row cell left parenthesis f plus g right parenthesis left parenthesis x right parenthesis end cell equals cell f left parenthesis x right parenthesis plus g left parenthesis x right parenthesis end cell row blank equals cell open parentheses fraction numerator 1 over denominator x plus 1 end fraction close parentheses plus open parentheses fraction numerator 5 x over denominator left parenthesis 2 x minus 4 end fraction close parentheses end cell row blank equals cell fraction numerator left parenthesis 2 x minus 4 right parenthesis plus 5 x left parenthesis x plus 1 right parenthesis over denominator open parentheses x plus 1 close parentheses left parenthesis 2 x minus 4 right parenthesis end fraction end cell row blank equals cell fraction numerator 2 x minus 4 plus 5 x squared plus 5 x over denominator 2 x squared minus 4 x plus 2 x minus 4 end fraction end cell row blank equals cell fraction numerator 5 x squared plus 7 x minus 4 over denominator 2 x squared minus 2 x minus 4 end fraction comma space untuk space x not equal to negative 1 space atau space x not equal to 2 end cell row blank blank blank row cell left parenthesis f minus g right parenthesis left parenthesis x right parenthesis end cell equals cell f left parenthesis x right parenthesis minus g left parenthesis x right parenthesis end cell row blank equals cell open parentheses fraction numerator 1 over denominator x plus 1 end fraction close parentheses minus open parentheses fraction numerator 5 x over denominator left parenthesis 2 x minus 4 end fraction close parentheses end cell row blank equals cell fraction numerator left parenthesis 2 x minus 4 right parenthesis minus 5 x left parenthesis x plus 1 right parenthesis over denominator left parenthesis x plus 1 right parenthesis left parenthesis 2 x minus 4 right parenthesis end fraction end cell row blank equals cell fraction numerator 2 x minus 4 minus 5 x squared minus 5 x over denominator 2 x squared minus 4 x plus 2 x minus 4 end fraction end cell row blank equals cell fraction numerator negative 5 x squared minus 3 x minus 4 over denominator 2 x squared minus 2 x minus 4 end fraction comma space untuk space x not equal to negative 1 space straight a straight t straight a straight u space x not equal to 2 end cell row blank blank blank row cell left parenthesis g minus f right parenthesis left parenthesis x right parenthesis end cell equals cell g left parenthesis x right parenthesis minus f left parenthesis x right parenthesis end cell row blank equals cell open parentheses fraction numerator 5 x over denominator left parenthesis 2 x minus 4 end fraction close parentheses minus open parentheses fraction numerator 1 over denominator x plus 1 end fraction close parentheses end cell row blank equals cell fraction numerator 5 x left parenthesis x plus 1 right parenthesis minus left parenthesis 2 x minus 4 right parenthesis over denominator left parenthesis x plus 1 right parenthesis left parenthesis 2 x minus 4 right parenthesis end fraction end cell row blank equals cell fraction numerator 5 x squared plus 5 x minus 2 x plus 4 over denominator 2 x squared minus 4 x plus 2 x minus 4 end fraction end cell row blank equals cell fraction numerator 5 x squared plus 3 x plus 4 over denominator 2 x squared minus 2 x minus 4 end fraction comma space untuk space x not equal to negative 1 space a t a u space x not equal to 2 end cell row blank blank blank row cell left parenthesis f cross times g right parenthesis left parenthesis x right parenthesis end cell equals cell f left parenthesis x right parenthesis cross times g left parenthesis x right parenthesis end cell row blank equals cell open parentheses fraction numerator 1 over denominator x plus 1 end fraction close parentheses cross times open parentheses fraction numerator 5 x over denominator left parenthesis 2 x minus 4 end fraction close parentheses end cell row blank equals cell fraction numerator 5 x over denominator left parenthesis x plus 1 right parenthesis left parenthesis 2 x minus 4 right parenthesis end fraction end cell row blank equals cell fraction numerator 5 x over denominator 2 x squared minus 4 x plus 2 x minus 4 end fraction comma space untuk space x not equal to negative 1 space atau space x not equal to 2 end cell row blank blank blank end table end style 

Dengan demikian, diperoleh rumusnya adalah , dan .

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