cho ham so y=f(x)=lx-4l=7 a) Tinh f(-1);f(3);f(4) b) tim cac gia tri cua x khi f(x)=7;f(x)=8

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1. Đáp án:

   $\begin{array}{l}
   f\left( x \right) = \left| {x – 4} \right| + 7\\
   a)f\left( { – 1} \right) = \left| { – 1 – 4} \right| + 7 = \left| { – 5} \right| + 7 = 5 + 7 = 12\\
   f\left( 3 \right) = \left| {3 – 4} \right| + 7 = \left| { – 1} \right| + 7 = 1 + 7 = 8\\
   f\left( 4 \right) = \left| {4 – 4} \right| + 7 = \left| 0 \right| + 7 = 0 + 7 = 7\\
   b)\\
    + )f\left( x \right) = 7 \Rightarrow \left| {x – 4} \right| + 7 = 7\\
    \Rightarrow \left| {x – 4} \right| = 0 \Rightarrow x = 4\\
    + )f\left( x \right) = 8\\
    \Rightarrow \left| {x – 4} \right| + 7 = 8\\
    \Rightarrow \left| {x – 4} \right| = 1\\
    \Rightarrow \left[ \begin{array}{l}
   x – 4 = 1\\
   x – 4 =  – 1
   \end{array} \right. \Rightarrow \left[ \begin{array}{l}
   x = 5\\
   x = 3
   \end{array} \right.
   \end{array}$

    

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