a)2*(x+1)-3*(x-2) = x-4 b)3*(4-x)-2*(x-1)=x+20 C)3*(x-2)+2x=10 d) Tìm x,y biết 3x+4y-xy=15

0 bình luận về “a)2*(x+1)-3*(x-2) = x-4 b)3*(4-x)-2*(x-1)=x+20 C)3*(x-2)+2x=10 d) Tìm x,y biết 3x+4y-xy=15”

1. $\begin{array}{l}a)\,\,2(x+1)-3(x-2)=x-4\\\Leftrightarrow 2x+2-3x+6=x-4\\\Leftrightarrow 2x-3x-x=-4-2-6\\\Leftrightarrow -2x=-12\\\Leftrightarrow x=6 \\\,\\b)\,\,3(4-x)-2(x-1)=x+20\\\Leftrightarrow 12-3x-2x+2=x+20\\\Leftrightarrow -3x-2x-x=20-12-2\\\Leftrightarrow -6x=6\\\Leftrightarrow x=-1 \\\,\\c)\,\,3(x-2)+2x=10\\\Leftrightarrow 3x-6+2x=10\\\Leftrightarrow 3x+2x=10+6\\\Leftrightarrow 5x=16\\\Leftrightarrow x=\dfrac{16}5 \\\,\\d)\,\,3x+4y-xy=15\\\Leftrightarrow x(3-y)+4y=15\\\Leftrightarrow x(3-y)-(12-4y)=15-12\\\Leftrightarrow x(3-y)-4(3-y)=3\\\Leftrightarrow (x-4)(3-y)=3 \\\text{mà $x,y\in\mathbb{Z}$} \\\to x-4,3-y \in Ư(3)=\{\pm1;\pm3\} \\\text{- Ta có bảng sau :} \\\begin{array}{|c|c|} \hline x-4&-3&-1&1&3 \\\hline 3-y&-1&-3&3&1 \\\hline x&1&3&5&7 \\\hline y&4&6&0&2 \\\hline \end{array} \\\text{- Vậy các cặp số $(x,y)$ tìm được là : $(1,4);(3,6);(5,0);(7,2)$} \end{array}$

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2. Đáp án:

    

   Giải thích các bước giải:

    a ) 2 ( x + 1 ) – 3 ( x – 2 ) = x – 4

   2x + 2 – 3x + 6 = x – 4

   2x – 3x – x = -4 – 2 – 6 

   -2x = -12

   x = 6

   b ) 3 ( 4 – x ) -2 ( x – 1 ) = x + 20

   12 – 3x -2x + 2 = x + 20

   -3x -2x -x = 20 – 12 -2

   -6x = 6

   x = – 1

   c ) 3 ( x – 2 ) + 2x = 10

   3x – 6 + 2x = 10

   3x + 2x = 10 +6

   5x = 16

   x = 16/5

   Câu d k biết 

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