unitsize(1 cm);

pair O, V, R;

O = (0,0);
V = (3,1);
R = reflect(O,(2,-1))*(V);

xaxis(-2,4);
yaxis(-3,1);

draw((-1)*(2,-1)--2*(2,-1));
draw(O--V,Arrow(8));
draw(O--R,Arrow(8));

dot(O);

label("$mathbf{v}$", (O + V)/2, N);
label("$mathbf{r}$", (O + R)/2, W);