Bài 1:tìm x a) 4×X–5×(-3+X)=7 b) 5×(X–7)+10×(3–X) =20 c) 7×(5–X) +5×(X–2)=15 *giúp với^^

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1. `1a)4.x-5.(-3+x)=7`

   `→4x+15-5x=7`

   `→4x-5x=7-15`

   `→-x=-8`

   `→x=8`

   Vậy `x=8`

   `b)5(x-7)+10(3-x)=20`

   `→5x-35+30-10x=20`

   `→5x-10x=20+35-30`

   `→-5x=25`

   `→x=25:(-5)`

   `→x=-5`

   Vậy `x=-5`

   `c)7(5-x)+5(x-2)=15`

   `→35-7x+5x-10=15`

   `→-7x+5x=15-35+10`

   `→-2x=-10`

   `→x=5`

   Vậy `x=5`

    

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2. Đáp án:

   ` a) 4×x–5×(-3+x)=7`

   `<=>4×x+15-5×x=7`

   `<=>-x=7-15`

   `<=>-x=-8`

   `<=>x=8`

   `b) 5×(x–7)+10×(3–x) =20`

   `<=>5×x-35+30-10×x=20`

   `<=>-5×x=20+35-30`

   `<=>-5×x=25`

   `<=>x=-5`

   `c) 7×(5–x) +5×(x–2)=15`

   `<=>35-7×x+5×x-10=15`

   `<=>-2×x=15-35+10`

   `<=>-2×x=-10`

   `<=>x=5`

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