一种函数的计算方法并给出相应的曲线图片

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var a, b, c;

function xtop(form) {

form.u.value = (form.b.value * -1) / (form.a.value * 2);

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function ytop(form) {

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function docoord(form) {

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<form>

<table bgcolor="#c0c0c0" cellspacing=2 cellpadding=2 border=3>

<tr>

<td>

<b>

<h3>parabolic calculator</h3>

<input name="a" size="3">x²+

<input name="b" size="3">x +

<input name="c" size="3">

<br>

<input type="button" value="x-top" name="x-top" onclick="xtop(this.form)">

<input type="button" value="y-top" name="y-top" onclick="ytop(this.form)">

<input type="button" value="crd" name="crd" onclick="docoord(this.form)">

<input type="button" value="disc." name="d" onclick="disc(this.form)">

<br>

<input type="button" value="0-points" name="zeroes" onclick="zeroes1(this.form);zeroes2(this.form)">

<input type="button" onclick="xtop(this.form);ytop(this.form);docoord(this.form);disc(this.form);zeroes1(this.form);zeroes2(this.form)" value="do all">

<input type="button" name="pics" value="show e.g." onclick="if(form.a.value>0 && form.o.value>0)move_in(p,p2.gif);if (form.a.value<0 && form.o.value>0)move_in(p,p3.gif); if(form.a.value>0 && form.o.value==0) move_in(p,p4.gif); if(form.a.value<0 && form.o.value==0) move_in(p,p5.gif); if(form.a.value>0 && form.o.value<0) move_in(p,p6.gif); if(form.a.value<0 && form.o.value<0) move_in(p,p7.gif)" value="show e.g.">

<br>

<input type="text" name="u" size="8"> x-top<br>

<input type="text" name="u2" size="8"> y-top<br>

<input type="text" size="8" name="co" onmouseover="form.rem.value=form.co.value"> coord.<br>

<input type="text" size="8" name="o"> discriminant<br>

<input type="text" size="8" name="n"> neg zero pt.<br>

<input type="text" size="8" name="n2"> pos zero pt.

<input type="hidden" value="" name="rem"><br>

<input type="reset" value="reset"><br>

</b>

</td>

<td><img src="p1.gif" width=200 name="p" height=200 border=0 alt=""></td>

</tr>

</table>

</form>