4/5 = 12/15=x/15 vậy x=12 bạn ạ 

\(\frac{4}{5}=\frac{x}{15}\)

\(\Rightarrow\frac{4}{5}=\frac{12}{15}=\frac{x}{15}\)( quy đồng)

=> x=12

tíc mình nha

\(\frac{4}{5}=\frac{x}{15}\)=> \(\frac{4}{5}=\frac{12}{15}\)

\(\frac{42}{x}=\frac{90}{105}\)=> \(\frac{42}{x}=\frac{6}{7}\)=> \(\frac{42}{49}=\frac{6}{7}\)

nha bn

\(\frac{4}{5}=\frac{x}{15}\Rightarrow x=\frac{4}{5}.15\Leftrightarrow x=12.\)

\(\frac{42}{x}=\frac{90}{105}\Leftrightarrow\frac{42}{x}=\frac{6}{7}\Leftrightarrow x=42:\frac{6}{7}\Leftrightarrow x=49\)

\(\frac{4}{5}=\frac{x}{15}\)

\(\Rightarrow\frac{4}{5}=\frac{12}{15}=\frac{x}{15}\)

\(\Rightarrow x=12\)

\(\frac{42}{x}=\frac{90}{105}\)

\(\Rightarrow\frac{42}{x}=\frac{6}{7}\)(rút gọn 90/105)

\(\Rightarrow\frac{42}{x}=\frac{42}{49}\)

\(\Rightarrow x=49\)

4/5=x/15

-->4/5=12/15(quy dong)

-->x=12

42/x=90/105

rut gon 90/105 = 6/7

42/x=6/7 

vi 42:6=7 nen 7x7=49

-->x=49

x=12

x=49

1)\(\frac{4}{5}=\frac{x}{15}\Rightarrow\frac{12}{15}=\frac{x}{15}\Rightarrow x=12\)

2) Ta có: \(\frac{90}{105}=\frac{6}{7}\)

\(\Rightarrow\frac{42}{x}=\frac{6}{7}\Rightarrow\frac{42}{x}=\frac{42}{49}\Rightarrow x=49\)

4/6= 10/15,42/49=90/105