tìm x biết a,|x-2|=3 b,|x-3|-7=13 c,-12(x-5)+7(3-x)=5

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1. a) |x – 2| = 3

   => x – 2 = 3 hoặc -3

   TH1 :

   x – 2 = 3

   x = 3 + 2 = 5

   TH2 :

   x – 2 = -3

   x = -3 + 2 = -1

   b) |x – 3| – 7 = 13

   |x – 3| = 13 + 7

   |x – 3| = 20

   => x – 3 = 20 hoặc -20

   TH1 :

   x – 3 = 20

   x = 20 + 3 = 23

   TH2 :

   x – 3 = -29

   x = -29 + 3 = -26

   c) -12(x – 5) + 7(3 – x) = 5

   -12x – (-60) + 21 – 7x = 5

   -12x + 60 + 21 – 7x = 5

   (-12x – 9x) + 60 + 21 = 5

   -21x + 81 = 5

   -21x = 5 – 81

   -21x = -76

   x = -76/-21

   x = 76/21

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2. a, |x-2|=3

   ⇔\(\left[ \begin{array}{l}x-2=3\\x-2=-3\end{array} \right.\)⇔\(\left[ \begin{array}{l}x=5\\x=-1\end{array} \right.\) 

   Vậy x=5 hoặc x=-1

   b, |x-3|-7=13

   ⇔|x-3|=20

   ⇔\(\left[ \begin{array}{l}x-3=20\\x-3=-20\end{array} \right.\)⇔\(\left[ \begin{array}{l}x=23\\x=-17\end{array} \right.\) 

   Vậy x=23 hoặc x=-17

   c, -12(x-5)+7(3-x)=5

   ⇔-12x+60+21-7x=5

   ⇔-12x-7x=5-60-21

   ⇔-19x=-76

   ⇔x=4

   Vậy x=4.

    

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