<html><head><meta http-equiv="Content-Type" content="text/html; charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">Hello,<div class=""><br class=""></div><div class="">%%%%%%%%%</div><div class=""><div style="margin: 0px; font-stretch: normal; line-height: normal; font-family: Monaco;" class="">\begin{center}</div><div style="margin: 0px; font-stretch: normal; line-height: normal; font-family: Monaco;" class="">\psset{xunit=1cm,yunit=0.5cm}</div><div style="margin: 0px; font-stretch: normal; line-height: normal; font-family: Monaco;" class="">\begin{pspicture*}(-3,-5)(6,6)</div><div style="margin: 0px; font-stretch: normal; line-height: normal; font-family: Monaco;" class="">\psgrid[gridlabels=0pt,subgriddiv=1,gridwidth=0.1pt]</div><div style="margin: 0px; font-stretch: normal; line-height: normal; font-family: Monaco;" class="">\psaxes[linewidth=1.25pt,Dx=10,Dy=10](0,0)(-3,-5)(6,6)</div><div style="margin: 0px; font-stretch: normal; line-height: normal; font-family: Monaco;" class="">\psaxes[linewidth=1.5pt]{->}(0,0)(1,1)</div><div style="margin: 0px; font-stretch: normal; line-height: normal; font-family: Monaco;" class="">\psplot[plotpoints=2000,linewidth=1.25pt,linecolor=red]{-2}{5}{x dup mul 3 mul 5 x mul sub 1 add}</div><div style="margin: 0px; font-stretch: normal; line-height: normal; font-family: Monaco;" class="">\psplotTangent[linecolor=blue]{0}{10}{x dup mul 3 mul 5 x mul sub 1 add}</div><div style="margin: 0px; font-stretch: normal; line-height: normal; font-family: Monaco;" class="">\psplotTangent[linecolor=blue]{2}{10}{x dup mul 3 mul 5 x mul sub 1 add}</div><div style="margin: 0px; font-stretch: normal; line-height: normal; font-family: Monaco;" class="">\uput[ur](0,1){A}\uput[r](2,3){B} \uput[l](1,-4){C}\uput[r](-0.7,5.5){\red $\mathcal{P}$}</div><div style="margin: 0px; font-stretch: normal; line-height: normal; font-family: Monaco;" class="">\end{pspicture*}</div><div style="margin: 0px; font-stretch: normal; line-height: normal; font-family: Monaco;" class="">\end{center}</div></div><div class="">%%%%%%%%%</div><div class="">Why the tangent in x = 0 is false ?</div><div class="">Thanks.</div><div class="">Denis</div></body></html>