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Diketahui f ( x ) = − 3 x + 2 2 b x 2 − a x + 5 ​ d an g ( x ) = a x 2 − b x + 3 ) − 4 x − 2 ​ . Jika nilai dari ( g ∙ f) ( 1) = 2 dan ( f ∙ g) ( 2) = -5 , maka nilai ( a ⋅ b ) 2 adalah ....

Diketahui   . Jika nilai dari (∙ f) (1) = 2  dan (∙ g) (2) = -5 , maka nilai   adalah ....

  1. -1

  2. 1

  3. negative 1 half 

  4. 1 half 

  5. 1 fourth 

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nilai .

nilai left parenthesis a cross times b right parenthesis squared equals open parentheses negative 1 half cross times left parenthesis negative 2 right parenthesis close parentheses squared equals left parenthesis 1 right parenthesis squared equals 1  .

Pembahasan

Ingat bahwa maka Kemudian, ingat bahwa f ∙ , maka Selanjutnya, kita lakukan proses eliminasi dengan menggunakan persamaan (1) dan (2). Lalu, subtitusikan nilai b = -2 ke persamaan (1) sehingga diperoleh Jadi, nilai .

Ingat bahwa left parenthesis g times f right parenthesis left parenthesis x right parenthesis equals g left parenthesis x right parenthesis times f left parenthesis x right parenthesis   maka

left parenthesis g times f right parenthesis left parenthesis 1 right parenthesis equals g left parenthesis 1 right parenthesis times f left parenthesis 1 right parenthesis 2 equals open parentheses fraction numerator negative 4 left parenthesis 1 right parenthesis minus 2 over denominator a left parenthesis 1 right parenthesis squared minus b left parenthesis 1 right parenthesis plus 3 end fraction close parentheses times open parentheses fraction numerator 2 b left parenthesis 1 right parenthesis squared minus a left parenthesis 1 right parenthesis plus 5 over denominator negative 3 left parenthesis 1 right parenthesis plus 2 end fraction close parentheses 2 equals fraction numerator negative 4 minus 2 over denominator a minus b plus 3 end fraction times fraction numerator 2 b minus a plus 5 over denominator negative 3 plus 2 end fraction 2 equals fraction numerator negative 6 over denominator a minus b plus 3 end fraction times fraction numerator 2 b minus a plus 5 over denominator negative 1 end fraction 2 equals fraction numerator 6 a minus 12 b minus 30 over denominator negative a plus b minus 3 end fraction minus 2 a plus 2 b minus 6 equals 6 a minus 12 b minus 30 space minus 8 a plus 14 b equals negative 24 space minus 4 a plus 7 b equals negative 12 horizontal ellipsis horizontal ellipsis horizontal ellipsis left parenthesis 1 right parenthesis 

Kemudian, ingat bahwafleft parenthesis f times g right parenthesis left parenthesis x right parenthesis equals f left parenthesis x right parenthesis times g left parenthesis x right parenthesis  , maka

left parenthesis f times g right parenthesis left parenthesis 2 right parenthesis equals f left parenthesis 2 right parenthesis times g left parenthesis 2 right parenthesis minus 5 equals open parentheses fraction numerator 2 b left parenthesis 2 right parenthesis squared minus a left parenthesis 2 right parenthesis plus 5 right parenthesis over denominator left parenthesis negative 3 left parenthesis 2 right parenthesis plus 2 right parenthesis end fraction close parentheses times open parentheses fraction numerator negative 4 left parenthesis 2 right parenthesis minus 2 over denominator a left parenthesis 2 right parenthesis squared minus b left parenthesis 2 right parenthesis plus 3 right parenthesis end fraction close parentheses minus 5 equals open parentheses fraction numerator 8 b minus 2 a plus 5 over denominator negative 6 plus 2 end fraction close parentheses times open parentheses fraction numerator negative 8 minus 2 over denominator 4 a minus 2 b plus 3 right parenthesis end fraction close parentheses minus 5 equals fraction numerator 8 b minus 2 a plus 5 over denominator negative 4 end fraction times fraction numerator negative 10 right parenthesis over denominator 4 a minus 2 b plus 3 end fraction minus 5 equals fraction numerator 20 a minus 80 b minus 50 over denominator negative 16 a plus 8 b minus 12 end fraction 80 a minus 40 b plus 60 equals 20 a minus 80 b minus 50 space 60 a plus 40 b equals negative 110 space 6 a plus 4 b equals negative 11 horizontal ellipsis horizontal ellipsis horizontal ellipsis left parenthesis 2 right parenthesis 

Selanjutnya, kita lakukan proses eliminasi dengan menggunakan persamaan (1) dan (2).

table row cell a left parenthesis 2 right parenthesis squared minus b left parenthesis 2 right parenthesis plus 3 right parenthesis end cell row cell a left parenthesis 2 right parenthesis squared minus b left parenthesis 2 right parenthesis plus 3 right parenthesis end cell end table open vertical bar table row cell cross times 3 end cell row cell cross times 2 end cell end table close vertical bar table row cell negative 12 a plus 21 b equals negative 36 end cell row cell bottom enclose 12 a plus 8 b equals negative 22 space plus end enclose end cell end table 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 space space space space space space space space space space space space space space space space space space space 29 b equals negative 58 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 space space space space space space space space space space space space space space space space space space space space space space space space b equals negative 2 

Lalu, subtitusikan nilai = -2  ke persamaan (1) sehingga diperoleh

negative 4 a plus 7 left parenthesis negative 2 right parenthesis equals negative 12 space minus 4 a minus 14 equals negative 12 space minus 4 a equals 2 space a equals negative 1 half 

Jadi, nilai left parenthesis a cross times b right parenthesis squared equals open parentheses negative 1 half cross times left parenthesis negative 2 right parenthesis close parentheses squared equals left parenthesis 1 right parenthesis squared equals 1  .

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