Vì 2020x=2019y=>\(\frac{x}{y}=\frac{2019}{2020}\)
Ta có:\(\frac{x}{zy}:\frac{y}{zx}=\frac{x}{zy}.\frac{zx}{y}=\frac{xzx}{zyy}=\frac{xx}{yy}=\left(\frac{x}{y^{ }}\right)^2\)
Thay \(\frac{x}{y}\)=\(\frac{2019}{2020}\),Ta có:\(\left(\frac{x}{y}\right)^2=\left(\frac{2019}{2020}\right)^2=\)~1