unitsize(1inch); path tri=(0,0)--(1,0)--(2,1)--cycle; pair p1=point(tri,0.5); pair p2=point(tri,1.5); pair z0=extension(p1,p1+I*dir(tri,0.5),p2,p2+I*dir(tri,1.5)); dot(z0); draw(circle(z0,abs(z0-point(tri,0)))); draw(tri,red);