u = 1cm;

beginfig(1);

pair A, B, C, M, N;
B=(0,0)*u; A=(1,4)*u; C=(5,0)*u; 
M=(2/3,8/3)*u; 
N=(2.33,2.67)*u;

draw A--B--C--cycle withpen pencircle scaled 1pt;
draw M--N withpen pencircle scaled 1pt;

label.top("A",A);
label.rt("C",C);
label.lft("B",B);
label.lft("M",M);
label.rt("N",N);

endfig;
end