Câu 1 : Tính hợp lý d, -7/9 . 3/11+ -7/9 . 8/11 + 1 7/9 (hỗn số 1 7/9) e, 7/35 . 10/19 + 7/35 . 9/19 – 2/35 f, (-25).125.4 . (-8).(-17) g, -3/4

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1. Đáp án:

    

   Giải thích các bước giải:

    d) $\frac{-7}{9}$ . $\frac{3}{11}$ + $\frac{-7}{9}$ . $\frac{8}{11}$ + 1$\frac{7}{9}$ 

   = $\frac{-7}{9}$ . $\frac{3}{11}$ + $\frac{-7}{9}$ . $\frac{8}{11}$ + $\frac{16}{9}$ 

   = $\frac{-7}{9}$ . ($\frac{3}{11}$ + $\frac{8}{11}$) + $\frac{16}{9}$

   =  $\frac{-7}{9}$ + $\frac{16}{9}$

   = 1

   e) $\frac{7}{35}$ . $\frac{10}{19}$ + $\frac{7}{35}$ . $\frac{9}{19}$ – $\frac{2}{35}$

   = $\frac{7}{35}$  . ($\frac{10}{19}$ + $\frac{9}{19}$) – $\frac{2}{35}$

   = $\frac{7}{35}$  x 1 – $\frac{2}{35}$

   = $\frac{7}{35}$ – $\frac{2}{35}$

   = $\frac{1}{7}$

   f) (-25) . 125 . 4 . (-8) . (-17)

   = [(-25) . 4] . [125 . (-8)] . (-17)

   = -100 . (-1000) x (-17)

   = 100000 x (-17)

   = -1700000

   g) -3/4 + 2/7 + -1/4 + 3/5 + 5/7

   = (2/7 + 5/7) + (-3/4 + -1/4) + 3/5

   =  1 + (-1) + 3/5 

   =  3/5

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2. Đáp án:

   $\text{ d) $\dfrac{-7}{9}$ . $\dfrac{3}{11}$ + (-$\dfrac{7}{9}$ ) . $\dfrac{8}{11}$ + 1$\dfrac{7}{9}$}$

   $\text{  = $\dfrac{-7}{9}$ . $\dfrac{3}{11}$ + (-$\dfrac{7}{9}$) . $\dfrac{8}{11}$ + $\dfrac{16}{9}$ }$

   $\text{ = $\dfrac{-7}{9}$ .( $\dfrac{3}{11}$ + $\dfrac{8}{11}$ ) + $\dfrac{16}{9}$ }$

   $\text{ = $\dfrac{-7}{9}$ + $\dfrac{16}{9}$}$

   $\text{ = 1 }$

   $\text{ e) $\dfrac{7}{35}$ . $\dfrac{10}{19}$ + $\dfrac{7}{35}$ . $\dfrac{9}{19}$ – $\dfrac{2}{35}$ }$

   $\text{  = $\dfrac{7}{35}$ . ($\dfrac{10}{19}$ + $\dfrac{9}{19}$) – $\dfrac{2}{35}$ }$

   $\text{  = $\dfrac{7}{35}$ . 1  -$\dfrac{2}{35}$ }$

   $\text{  = $\dfrac{1}{7}$ }$

   $\text{ f (-25) . 125 . 4 . (-8) . (-17) }$

   $\text{ = [ (-25) . 4] . [ 125 . (-8) ] . (-17) }$

   $\text{  = -100 . (-1000) . (-17) }$

   $\text{ = -1700000 }$

   $\text{ g , $\dfrac{-3}{4}$ + $\dfrac{2}{7}$ + (-$\dfrac{1}{4}$) + $\dfrac{3}{5}$ + $\dfrac{5}{7}$ }$

   $\text{  = ( $\dfrac{-3}{4}$ – $\dfrac{1}{4}$) + ($\dfrac{2}{7}$ + $\dfrac{5}{7}$) + $\dfrac{3}{5}$ }$

   $\text{  = -1 + 1 + $\dfrac{3}{5}$ }$

   $\text{  = 0 + $\dfrac{3}{5}$ }$

   $\text{ = $\dfrac{3}{5}$ }$

    

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