\(\frac{37-x}{x+13}=\frac{3}{7}\)

\(\Leftrightarrow3.\left(x+13\right)=7.\left(37-x\right)\)

\(\Leftrightarrow3.x+13.3=7.37-7.x\)

\(\Leftrightarrow3x+39=-7x+259\)

\(\Leftrightarrow3x+7x=259-39\)

\(\Leftrightarrow10x=220\)

\(\Leftrightarrow x=22\)

$\frac{37-x}{x+13}=\frac{3}{7}$

\(\frac{37-x}{x+13}=\frac{3}{7}\)

\(\Leftrightarrow\left(37-x\right).7=3.\left(x+13\right)\)

\(\Leftrightarrow259-7x=3x+39\)

\(\Leftrightarrow10x=220\)

\(\Leftrightarrow x=22\)

Vậy ... 

Bài còn lại tương tự 

\(\Leftrightarrow7\left(37-x\right)=3\left(x+13\right)\Leftrightarrow259-7x=3x+39\Leftrightarrow259-39=3x+7x\)

\(10x=220\Leftrightarrow x=22\)

(37-x) . 7 =3. (x+13)

=>259 -7x=3x+39

=>.259-39=3x+7x

=>220=10x

=>x=22

\(\frac{37-x}{x+13}=\frac{3}{7}\)

=> 3.(x+13)=7.(37-x)

=> 3x+39= 259-7x

=> 3x+7x=259-39

=> 10x= 220

=> x=22

\(\frac{a}{b}\) ai bày mk viết phân số với

=> (37  - x) . 7 = (x + 13) . 3

259 - 7x = 3x + 39

-7x - 3x = 39 - 259

-10x = -220

x =22          

=> (37-x).7=(x+13).3

=> 259-7x=3x+39

=> -7x-3x=39-259

=> -10x=-220

=> x=-220:(-10)

=> x=22

a) 0,4:x=x:0,9

0,4.0,9=x²

0,36 =x²

\(\sqrt{0,36}\)=x

0,6 =x

a) 0,4 : x = x : 0,9 x^2=0,9 . 0,4 x^2=(0,6)^2 =>x=+_6