# Change Equation of a Graph

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This example shows how you can change the equation of a graph without creating the whole construction again. <div style="width:960px"> <div id="jxgbox" class="jxgbox" style="width:600px; height:400px; float:left; "></div> <p style="float:right"> <input type="text" id="eingabe" value="Math.sin(x)*Math.cos(x)"> <input type="button" value="set" onClick="doIt()" style='margin:1em'> </p> </div> <br clear=all> <div id="debug" style="display:none;"></div> <script type="text/javascript"> /* <![CDATA[ */ board = JXG.JSXGraph.initBoard('jxgbox', {originX: 250, originY: 250, unitX: 40, unitY: 20}); // Axes b1axisx = board.createElement('axis', [[1,0], [0,0]], {}); b1axisy = board.createElement('axis', [[0,1], [0,0]], {}); eval("function f(x){ return "+document.getElementById("eingabe").value+";}"); graph = board.createElement('curve', [function(x){ return x; }, function(x){ return f(x); }, "x", -10, 10]); //graph = eval("board.createElement('curve', [function(x){ return x; }, function(x){ return "+document.getElementById("eingabe").value+";}, 'x', -10, 10])"); //graph.curveType = "graph"; p1 = board.createElement('glider', [graph], {style:6, name:'P'}); g = board.algebra.D(f); p2 = board.createElement('point', [function() { return p1.X()+1;}, function() {return p1.Y()+board.algebra.D(graph.Y)(p1.X());}], {style:1, name:''}); l1 = board.createElement('line', [p1,p2],{}); p3 = board.createElement('point', [function() { return p2.X();}, function() {return p1.Y();}],{style:1, name:''}); pol = board.createElement('polygon', [p1,p2,p3], {}); t = board.createElement('text', [function(){return p1.X()+1.1;},function(){return p1.Y()+(p2.Y()-p3.Y())/2;},function(){ return "m="+(board.round(p2.Y()-p3.Y(),2));}]); function doIt(){ eval("function f(x){ return "+document.getElementById("eingabe").value+";}"); graph.yterm = function(x){ return f(x); }; // usually: e.g. "x^2" //graph.yterm = eval("function(x){ return "+document.getElementById("eingabe").value+"; };"); graph.Y = graph.yterm; graph.updateCurve(); board.update(); } /* ]]> */ </script>