2/5=12/x 3+13x/17=3/4 7/x+6=4/28 1/21=28/x 7/4=x/28 6/13=x/-26 mn giúp mình với

$\dfrac{2}{5}=\dfrac{12}{x}$

$→\dfrac{2x}{5}=12$

$→2x=12\:.\:5$

$→2x=60$

$→x=30$

`Vậy` $x=30$

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$3+\dfrac{13x}{17}=\dfrac{3}{4}$

$→\dfrac{13}{17}x=\dfrac{-9}{4}$

$→13x=-\dfrac{153}{4}$

$→x=-\dfrac{\dfrac{153}{4}}{13}$

$→x=-\dfrac{153}{52}$

`Vậy` $x=-\dfrac{153}{52}$

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$\dfrac{7}{x}+6=\dfrac{4}{28}$

$→\dfrac{7}{x}+6=\dfrac{1}{7}$

$→\dfrac{7}{x}=\dfrac{1}{7}-6$

$\dfrac{7}{x}=-\dfrac{41}{7}$

$→7=-\dfrac{41x}{7}$

$→7\:.\:7=−41x$

$→49=−41x$

$→x=-\dfrac{49}{41}$

`Vậy` $x=-\dfrac{49}{41}$

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$\dfrac{1}{21}=\dfrac{28}{x}$

$→\dfrac{x}{21}=28$

$→x=28\:.\:21$

$→x=588$

`Vậy` $x=588$

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$\dfrac{7}{4}=\dfrac{x}{28}$

$→x=\dfrac{28\:.\:7\:}{4}$

$→x=\dfrac{196}{4}$

$→x=49$

`Vậy` $x=49$

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$\dfrac{6}{13}=\dfrac{x}{-26}$

$→x=\dfrac{-26\cdot \:6}{13}$

$→x=-\dfrac{156}{13}$

`Vậy` $x=-12$

Đáp án:

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