u := 1cm;

pair A,B,C,D,E;
numeric height, width;
height := 2.8;
width := 4.5;

B := origin;
A := (B+(0,height))*u;
D := (B+(width,0))*u;
E := (xpart(D),ypart(A));
C := point 0.6length(B--D) of (B--D);

path rect, tri;
rect := B -- A -- E -- D;
tri := B -- C -- E .. cycle;

draw rect dashed evenly;
draw D -- C;
draw tri withpen pencircle scaled 1.2pt withcolor 0.5blue;
fill tri withcolor (0,1,1);

pair h;
h := point 0.5length(E--D) of (E--D);

label.llft(btex B etex, B);
label.urt(btex E etex, E);
label.lrt(btex D etex, D);
label.bot(btex C etex, C);
label.rt(btex $h$ etex, h);