Tìm x, biết a) x + 30%x = -1,3 b) ( 2x + 3/4 ) ( $x^{2}$ – 1/9 ) = 0 c) 7 ║ 3/5x – 40% ║ – 3/5 : 1/2 = 0,2 d) x-5/8 = 2/x-5

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1.  a) x+30%x=−1,3x+30%x=-1,3

   ⇔1310x=−1,3⇔1310x=-1,3

   ⇔x=−1⇔x=-1

   Vậy x=−1x=-1

   b) (2x+34)(x2−19)=0(2x+34)(x2-19)=0

   ⇔⇔ ⎡⎢ ⎢⎣2x+34=0x2−19=0[2x+34=0x2−19=0

   ⇔⇔ ⎡⎢ ⎢⎣x=−38x=29[x=−38x=29 

   Vậy S=−38;29S=−38;29

   c) 7∣∣∣35x−40%∣∣∣−35:12=0,27|35x-40%|-35:12=0,2

   ⇔7∣∣∣35x−40%∣∣∣−65=0,2⇔7|35x-40%|-65=0,2

   ⇔7∣∣∣35x−40%∣∣∣=75⇔7|35x-40%|=75

   ⇔∣∣∣35x−40%∣∣∣=15⇔|35x-40%|=15

   ⇔⇔⎡⎢ ⎢⎣35x−25=1535x−25=−15[35x−25=1535x−25=−15

   ⇔⇔ ⎡⎣x=1x=13[x=1x=13 

   Vậy S={1;13}S={1;13}

   d) x−58=2x−5x-58=2x-5

   ⇔(x−5)2=16⇔(x-5)2=16

   ⇔x2−5x−5x+25=16⇔x2-5x-5x+25=16

   ⇔x2−10x+9=0⇔x2-10x+9=0

   ⇔x2−x−9x+9=0⇔x2-x-9x+9=0

   ⇔x(x−1)−9(x−1)=0⇔x(x-1)-9(x-1)=0

   ⇔(x−9)(x−1)=0⇔(x-9)(x-1)=0

   ⇔⇔ [x−9=0x−1=0[x−9=0x−1=0

   ⇔⇔ [x=9x=1[x=9x=1 

   Vậy S={9;1}

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