code for diagram

> f:=x->abs(2-x)/6+sqrt(x^2+4^2)/4:
plotf:=plot({f(x),0},x=1..3):
dotline:=plot([[2,0],[2,f(2)]],thickness=3,linestyle=3):
txt:=plots[textplot]([2,-.2,`a`],font=[TIMES,BOLD,16]):
plots[display]({plotf,dotline,txt},xtickmarks=[],
ytickmarks=[],scaling=constrained);