[code]f(x)=Polynomial({A,B,C,D,E})[br]list1=Join({{Extremum(f)},{Root(f)},{(0,f(0))}})[br]P'=Point(f)[br]Q=ClosestPoint(list1,P')[br]d=AxisStepX()/20[br]P=DynamicCoordinates(P',[br] If(Distance(P',Q)[br][/code]

gMath 互動數學教室 [url=http://www.geogebra.hk/]http://www.geogebra.hk[/url]