Answer
$\sqrt 5$
Work Step by Step
$d(P_1,P_2)=\sqrt {(x_2-x_1)^2+(y_2-y_1)^2}$ $d((0,0),(-2,1))=\sqrt {(-2-0)^2+(1-0)^2}=\sqrt {4+1}=\sqrt 5$
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