\(\dfrac{a}{12}=\dfrac{b}{9}=\dfrac{c}{5}\)
\(\Rightarrow a=12k\)
\(\Rightarrow b=9k\)
\(\Rightarrow c=5k\)
\(\Rightarrow a.b.c=12k.9k.5k=20\)
\(\Rightarrow540.k^3=20\)
\(\Rightarrow k^3=\dfrac{1}{27}\)
\(\Rightarrow k=\dfrac{1}{3}\)
\(a=\dfrac{1}{3}.12=4\)
\(b=\dfrac{1}{3}.9=3\)
\(c=\dfrac{1}{3}.5=\dfrac{5}{3}\)
Ta có : \(\dfrac{a}{12}\)=\(\dfrac{b}{9}\)=\(\dfrac{c}{5}\)=k
=> a= k.12
=>b=k.9
=> c= k.5
Mà a.b.c=20
=> k.12 .k.9.k.5 = 20
=> k3.540 =20
=> k3 = \(\dfrac{1}{27}\)
=> k=\(\dfrac{1}{3}\)
Vì a= k.12 => a= \(\dfrac{1}{3}\).12 => a = 4
b= k.9 => b= \(\dfrac{1}{3}\).9 => b= 3
c=k.5 => c=\(\dfrac{1}{3}\) .5 => c =\(\dfrac{5}{3}\)
Vậy ......................
