## Precalculus: Concepts Through Functions, A Unit Circle Approach to Trigonometry (3rd Edition)

$\sqrt{10}$
$(x_{1},y_{1}) = (1,1)$ $(x_{2},y_{2}) = (-2,2)$ $[d(P_1,P_2)]^{2} =(x_{2}-x_{1})^{2}+(y_{2}-y_{1})^{2} =(-2-1)^{2}+(2-1)^{2}= 9+1=10$ $d(P_1,P_2) =\sqrt{10}$