1. Tính nhanh a. -1/24 -[1/4 – ( 1/2 – 7/8 ) ] b. ( -3/4 + 5/13 ) : 2/7 – ( 2 1/4 + 8/13 ) :2/7

0 bình luận về “1. Tính nhanh a. -1/24 -[1/4 – ( 1/2 – 7/8 ) ] b. ( -3/4 + 5/13 ) : 2/7 – ( 2 1/4 + 8/13 ) :2/7”

1. `text{Đáp án:}`

   `=-2/3`

   `=-147/13`

   `text{Giải thích các bước giải:}`

   `text{1. Tính }`
   `a.` 
   `-1/24 -[1/4 – ( 1/2 – 7/8 ) ]`
   `=-1/24-[1/4-(4/8-7/8)]`
   `=-1/24-[1/4-(-3)/8]`
   `=-1/24-[1/4+3/8]`
   `=-1/24-[2/8+3/8]`
   `=-1/24-5/8`
   `=-1/24-15/24`
   `=(-1-15)/24`
   `=-16/24`

   `=-2/3`
   `b.`
   `( -3/4 + 5/13 ) : 2/7 – ( 2  1/4 + 8/13 ) :2/7`
   `=( -3/4 + 5/13 ) : 2/7 – ( 9/4 + 8/13 ) :2/7`
   `=( -3/4 + 5/13 ) . 7/2 – ( 9/4 + 8/13 ). 7/2`
   `=7/2.{[-3/4+5/13]-[9/4+8/13]}`
   `=7/2.{-3/4+5/13-9/4-8/13}`
   `=7/2.{(-3/4-9/4)+(5/13-8/13)}`
   `=7/2.{-12/4+(-3)/13}`
   `=7/2.{-3+(-3)/13}`
   `=7/2.{-39/13+(-3)/13}`
   `=7/2.(-42)/13`
   `=-294/26`

   `=-147/13`

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2. a) $-\dfrac{1}{24}-[\dfrac{1}{4}-(\dfrac{1}{2}-\dfrac{7}{8})]$

   $=-\dfrac{1}{24}-\dfrac{6}{24}+\dfrac{12}{24}-\dfrac{21}{24}$

   $=\dfrac{-1-6+12-21}{24}=\dfrac{-16}{24}=\dfrac{-2}{3}$

   b) $(-\dfrac{3}{4}+\dfrac{5}{13}):\dfrac{2}{7}-(2\dfrac{1}{4}+\dfrac{8}{13}):\dfrac{2}{7}$

   $=(-\dfrac{3}{4}+\dfrac{5}{13}).\dfrac{7}{2}-(\dfrac{9}{4}+\dfrac{8}{13}).\dfrac{7}{2}$

   $=\dfrac{7}{2}.(-\dfrac{3}{4}+\dfrac{5}{13}-\dfrac{9}{4}-\dfrac{8}{13})$

   $=\dfrac{7}{2}.[(-\dfrac{3}{4}-\dfrac{9}{4})+(\dfrac{5}{13}-\dfrac{8}{13})]$

   $=\dfrac{7}{2}.[-3-\dfrac{3}{13}]$

   $=\dfrac{7}{2}.(-\dfrac{42}{13})$

   $=-\dfrac{147}{13}$

   Lưu ý: Có khả năng không thể tính nhanh vì tính nhanh thường là để sẽ ra các chữ số thuộc số nguyên

    

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