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222-9+11+12:2*14+14 = ? ( )

Toán Lớp 9: Tìm `f(x) `biết `f(x – 1) = x^2 + 3x – 2.`

Toán Lớp 9: Tìm f(x) biết f(x – 1) = x^2 + 3x – 2.

Comments ( 2 )

  1. $\begin{array}{l} f\left( {x – 1} \right) = {x^2} + 3x – 2\\ f\left( {x – 1} \right) = {x^2} – 2x + 1 + 5x – 3\\ f\left( {x – 1} \right) = {\left( {x – 1} \right)^2} + 5\left( {x – 1} \right) + 2\\  \Rightarrow f\left( x \right) = {x^2} + 5x + 2 \end{array}$  

  2. Ta có:  f(x-1)=x^2 + 3x – 2
    Đặt t=x-1⇔x=t+1
    =>f(t)=(t+1)^2 + 3(t+1)-2=t^2 + 5t +2
    =>f(x)=x^2 + 5x – 2
    Vậy….

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222-9+11+12:2*14+14 = ? ( )

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