\(\frac{4}{7}=\frac{x}{21}\Rightarrow7x=21\cdot4\)
\(\Rightarrow7x=84\)
\(\Rightarrow x=12\)
4/7=x/21
=>x=4/7x21
=>x=12
Trả lời: x=12
\(\frac{4}{7}=\frac{x}{21}\)
\(x\left(-\infty;\infty\right)\)
\(\frac{4}{7}=\frac{x}{21}\Rightarrow4.21=7x\)
\(\frac{4.21}{7}=\frac{7x}{7}\)
\(\frac{4.21}{7}=x\)
\(x=12\)
ta có :
\(\frac{4}{7}=\frac{x}{21}\)
quy đồng phân số 4/7
\(\frac{12}{21}=\frac{x}{21}\)
\(\Rightarrow x=12\)