## Precalculus (6th Edition)

$\color{blue}{-\dfrac{4}{7}}$
Since $\dfrac{16}{49} = \left(\dfrac{4}{7}\right)^2$, the given expression simplifies to: $=-\sqrt{\left(\dfrac{4}{7}\right)^2} \\=\color{blue}{-\dfrac{4}{7}}$