`\sqrt{\frac{16x^3}{49y}}`
`= \frac{\sqrt{16x^3}}{\sqrt{49y}}`
`= \frac{2^2 x\sqrt{x}}{7\sqrt{y}}`
`= \frac{4x\sqrt{x}}{7\sqrt{y}}`(vì `x\ge0, y>0`)
`= \frac{4x\sqrt{x}}{7\sqrt{y}}.\frac{\sqrt{y}}{\sqrt{y}}`
`= \frac{4x\sqrt{x}\sqrt{y}}{7\sqrt{y}\sqrt{y}}`
`= \frac{4x\sqrt{xy}}{7y}`
