Question

\(\dfrac{40}{x-30}=\dfrac{20}{y-15}=\dfrac{28}{z-21}vàx.y.z=22400\)

Answer 1

\(\dfrac{40}{x-30}=\dfrac{20}{y-15}=\dfrac{28}{z-21}\Leftrightarrow\dfrac{x-30}{40}=\dfrac{y-15}{20}=\dfrac{z-21}{28}\)

\(\Leftrightarrow\dfrac{x}{40}-\dfrac{3}{4}=\dfrac{y}{20}-\dfrac{3}{4}=\dfrac{z}{28}-\dfrac{3}{4}\Leftrightarrow\dfrac{x}{40}=\dfrac{y}{20}=\dfrac{z}{28}\)

Đặt \(\dfrac{x}{40}=\dfrac{y}{20}=\dfrac{z}{28}=t\)

Suy ra \(x=40t,y=20t,z=28t\).

\(xyz=40t.20t.28t=22400t^3=22400\Leftrightarrow t=1\).

Suy ra \(x=40,y=20,z=28\).