A B C isosceles
H = projection(C, line(A, B))
draw(A, B, C)
draw(H)
draw(segment(C, H), dashed)
mark(B, H, C, right)
mark(segment(A, H))
mark(segment(B, H))
mark(segment(A, C), cross)
mark(segment(C, B), cross)
mark(B, A, C, double)
mark(C, B, A, double)