beginfig(1);
u:=1cm;
z0=(0,0);
z1=z0+4u*dir0;
z2=z0+2u*dir45;
draw z0--z1--z2--cycle;
label.bot("4", 0.5[z0,z1]);
label.ulft("2", 0.5[z0,z2]);
label.urt(btex$b$etex, 0.5[z1,z2]);
label(btex$45^\circ$etex, z0+0.7cm*dir(45/2));
label(btex$C$etex, z2+0.35cm*dir-90);
label(btex$A$etex, z1+1cm*dir(180-14.4));
endfig;

bye