#### Answer

$$2.8$$

#### Work Step by Step

The distance $d$ between the two points $(x_{1},y_{1})$ and $(x_{2},y_{2})$ is given by
$$d=\sqrt {(x_{2}-x_{1})^{2} + (y_{2}-y_{1})^{2}}.$$
Substitute $x_{1}=-1$, $y_{1}=1$, $x_{2}=1$ and $y_{2}=-1$ and round to the nearest tenth.
$$d=\sqrt {(1-(-1))^{2}+(-1-1)^{2}}=\sqrt {4+4}=\sqrt{8}=2.8$$