beginfig(5); input angles; u=1 cm; z0=(1u,1u); z1=(3u,1u); drawarrow z0..z1 ; z2-z0 =(z1-z0) rotated 60; drawarrow z0..z2; draw z1{up}..z2 dashed evenly; z3=0.3[z0,z1]; z4=0.3[z0,z2]; drawarrow z3{up}..z4; %mark_angle(z1,z0,z2,0); draw_marked(z0--z1,2); draw_marked(z0--z2,2); dotlabel.bot(btex $O$ etex, z0); label.bot(btex $M$ etex, z1); label.top(btex $M'$ etex, z2); z5=(1.8u,1.3u); label.top(btex $\alpha$ etex, z5); z6=(2u,0.5u); label.bot(btex $\alpha={\pi\over 3}$ etex, z6); endfig; end