`b)` `5/4` `và` `5/6`

`\text{Ta có :}` 

`5/4` `=` $\dfrac{5×3}{4×3}$ `=` `15/12`

`5/6` `=` $\dfrac{5×2}{6×2}$ `=` `10/12`

`\text{Vậy 2 phân số}` `5/4` `và` `5/6` `\text{sau khi quy đồng là :}` `15/12` `và` `10/12`

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`c)` `1/2` `:` `2/3` `và` `1/6`

Ta có : `1/2` `:` `2/3` `=` `3/4`

`3/4` `=` $\dfrac{3×3}{4×3}$ `=` `9/12`

`1/6` `=` $\dfrac{1×2}{6×2}$ `=` `2/12`     

`\text{Vậy 2 phân số}` `1/2` `:` `2/3` `và` `1/6` `\text{sau khi quy đồng là :}` `9/12` `và` `2/12`

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`Tính` `:`

`a)` $\dfrac{3×4×7}{5× 3× 4}$ `=` `7/5`

`b)` $\dfrac{2×5×6×8}{6×2×8×9}$ `=` `5/9`  

`c)` $\dfrac{4×5×6}{3×8×10}$ `=` `1/2`

`@` `\text{Giải thích : Ta lược bỏ thừa số chung ở cả tử và mẫu.}`

`a)` $\dfrac{3×4×7}{5× 3× 4}$ `=` `(\cancel{3} xx \cancel{4} xx 7)/(5 xx \cancel{3} xx \cancel{4})` `=` `7/5`

`b)`  $\dfrac{2×5×6×8}{6× 2× 8×9}$ `=` `(\cancel{2} xx 5 xx \cancel{6} xx \cancel{8})/(\cancel{6} xx \cancel{2} xx \cancel{8}xx9)` `=` `5/9`

`c)` $\dfrac{4×5×6}{3× 8×10}$ `=`  `(\cancel{4} xx \cancel{5} xx \cancel{3} xx \cancel{2})/(\cancel{3} xx \cancel{4} xx \cancel{2}xx\cancel{5}xx2)` `=` `1/2`

b)

$\dfrac{5}{4}$ = $\dfrac{15}{12}$

$\dfrac{5}{6}$ = $\dfrac{10}{12}$

c)

$\dfrac{1}{2}$ : $\dfrac{2}{3}$ = $\dfrac{3}{4}$ = $\dfrac{9}{12}$

                                                   $\dfrac{1}{6}$ = $\dfrac{2}{12}$

Bài . Tính :

a)

$\dfrac{3 x 4 x 7}{5 x 3 x 4}$ = $\dfrac{7}{5}$ ( rút gọn 3 ; 4 )

b)

$\dfrac{2 x 5 x 6 x 8}{6 x 2 x 8 x 9}$ = $\dfrac{5}{9}$ ( rút gọn 2 ; 6 ; 8 )

c)

$\dfrac{4 x 5 x 6}{3 x 8 x 10}$ = $\dfrac{4 x 5 x 3 x 2}{3 x 4 x 2 x 5 x 2}$ = $\dfrac{2}{2 x 2}$ = $\dfrac{1}{2}$ ( rút gọn 3 ; 4 ; 5 )

XIN HAY NHẤT !