Tìm x biết a,|x+5|=100 b,100 – | 25-x | = 40 c,|2x+1| = | 23-x | d,|11-7x| – | 4x + 3|=0

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1. a) | x+5 | = 100

     => x + 5 = 100 hoặc -100

   +) Nếu x + 5 = 100

               x = 100 – 5

               x = 95 

   +) Nếu x + 5 = -100

               x = -100 – 5

               x = -105

   b) 100 – | 25 – x | = 40

       | 25 – x | = 100 – 40

       | 25 – x | = 60

   => 25 – x = 60 hoặc -60

   +) Nếu 25 – x = 60

               x = 25 – 60 

               x = -35

   +) Nếu 25 – x = -60

                x = 25 – ( -60 )

                x = 85

   c) + d) mik ko bt làm 🙁

    

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2. a. |x+5|=100

   ⇒ [x+5=100x+5=−100[x+5=100x+5=−100 

   ⇒ [x=100−5x=−100−5[x=100−5x=−100−5 

   ⇒ [x=95x=−105[x=95x=−105 

   b. 100-| 25-x | = 40

   ⇒ | 25-x | =100-40

   ⇒ | 25-x | =60

   ⇒ [25−x=6025−x=−60[25−x=6025−x=−60 

   ⇒ [x=25−60x=25−(−60)[x=25−60x=25−(−60) 

   ⇒ [x=−35x=85[x=−35x=85 

   c. |2x+1| = | 23-x |

   ⇒ [2x+1=23−x2x+1=−(23−x)[2x+1=23−x2x+1=−(23−x) 

   ⇒ [2x+x=23−12x+1=−23+x[2x+x=23−12x+1=−23+x 

   ⇒ [3x=222x−x=−23−1[3x=222x−x=−23−1 

   ⇒ [x=223x=−24[x=223x=−24 

   d. |11-7x| – | 4x + 3|=0

   ⇒ |11−7x|=|4x+3||11−7x|=|4x+3|

   ⇒ [11−7x=4x+311−7x=−(4x+3)[11−7x=4x+311−7x=−(4x+3) 

   ⇒ [7x−4x=3−1111−7x=−4x−3[7x−4x=3−1111−7x=−4x−3 

   ⇒ [3x=−84x−7x=−3−11[3x=−84x−7x=−3−11 

   ⇒ [x=−83−3x=−14[x=−83−3x=−14 

   ⇒ [x=−83x=143[x=−83x=143 

    

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