[tex]\frac{a}{b}=\frac{30}{4}=\frac{15}{2}[/tex]
Do [tex] GCD(a, b)=5\Rightarrow \left\{\begin{matrix} a=5i\\b=5k \end{matrix}\right.(GCD(i, k )=1)[/tex]
Vì [tex]\frac{a}{b}=\frac{i}{k}=\frac{15}{2}; GCD(i, k )=1[/tex]
[tex]\Rightarrow \left\{\begin{matrix} i=15\\k=2 \end{matrix}\right.[/tex]
[tex]\Rightarrow \left\{\begin{matrix} a=75\\b=10 \end{matrix}\right.[/tex]
P/s: GCD là ƯCLN nha...