a /x – 12 : x – 5 b/2x +7 : x + 3 c/ 4x + 21 : x + 1 d/36 : 2x – 1

0 bình luận về “a /x – 12 : x – 5 b/2x +7 : x + 3 c/ 4x + 21 : x + 1 d/36 : 2x – 1”

1. Đáp án:

    a: x-12 : x-5

   = (x:x)-12-5

   =1-12-5

   =-16

   b: 2x +7 : x +3

   =(2x :x)+7+3

   =2x+10

   =2(x+5)

   c: 4x + 21 :x+1

   =(4x:x)+21+1

   =4x+21+1

   =4x+22

   =2(2x+11)

   d: 36:2x-1

   =(36 :2x)-1

   =2(18:x)-1

   =18:x

    

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2. Cách giải:

   $a,x-12 \vdots x-5$

   $\to x-5-7 \vdots x-5$

   $\to 7 \vdots x-5$

   $\to x-5 \in Ư(7)={1,-1,7,-7}$

   $\to x \in {6,4,12,-2}$

   $b,2x+7 \vdots x+3$

   $\to 2(x+3)+1 \vdots x+3$

   $\to 1 \vdots x+3$

   $\to x+3 \in Ư(1)={1,-1}$

   $\to x \in {-2,-4}$

   $c,4x+21 \vdots x+1$

   $\to 4(x+1)+17 \vdots x+1$

   $\to 17 \vdots x+1$

   $\to x+1 \in Ư(17)={1,-1,17,-17}$

   $\to x \in {0,16,-18,-2}$

   $36 \vdots 2x-1$

   $\to 2x-1 \in Ư(36)={1,-1 2,-2,3,-3,4,-4,6,-6,9,-9,12,-12,18,-18,36,-36}$

   Mà 2x-1 là số lẻ

   $\to 2x-1 \in {1,-1,3,-3,9,-9}$

   $\to 2x \in {0,2,4,-2,10,-8}$

   $\to x \in {0,1,2,-1,5,-4}$

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