a

\(=\sqrt{\left(\frac{x}{y}\right)^2+\left(\frac{y}{x}\right)^2-2.\frac{x}{y}.\frac{y}{x}}-\sqrt{\left(\frac{x}{y}\right)^2+\left(\frac{y}{x}\right)^2+2.\frac{x}{y}.\frac{y}{x}}\)

\(=\sqrt{\left(\frac{x}{y}-\frac{y}{x}\right)^2}-\sqrt{\left(\frac{x}{y}+\frac{y}{x}\right)^2}\)

\(=\left|\frac{x}{y}-\frac{y}{x}\right|-\left|\frac{x}{y}+\frac{y}{x}\right|\)

Cảm ơn cô