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midpoint_formula.html
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midpoint_formula.html
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<!DOCTYPE html>
<html data-require="math graphie">
<head>
<meta charset="UTF-8" />
<title>Midpoint formula</title>
<script src="../khan-exercise.js"></script>
<script>
var point1Style = {
color : "#6495ED",
stroke : "#6495ED",
fill : "#6495ED"
};
var point2Style = {
color : "#28AE7B",
stroke : "#28AE7B",
fill : "#28AE7B",
strokeWidth: 1.5
};
var midPtStyle = {
color : "#FFA500",
stroke : "#FFA500",
fill : "#FFA500",
strokeWidth: 1.5
};
function getPos( refPoint, otherPoint ) {
var pos = "";
if( refPoint[1] > otherPoint[1] ) {
pos += "above";
} else {
pos += "below";
}
if( refPoint[0] !== otherPoint[0] ) {
pos += " ";
}
if( refPoint[0] > otherPoint[0] ) {
pos += "right";
} else {
pos += "left";
}
return pos;
}
</script>
</head>
<body>
<div class="exercise">
<div class="vars" data-ensure="X1 < X2 && Y1 !== Y2">
<var id="X1" data-ensure="X1 < 0 || X1 > 2">randRange( -8, 7 )</var>
<var id="X2" data-ensure="X2 > 0 || X2 < -2">randRange( -7, 8 )</var>
<var id="Y1" data-ensure="abs( Y1 ) > 1">randRange( -9, 8 )</var>
<var id="Y2" data-ensure="abs( Y2 ) > 1">randRange( -9, 8 )</var>
<var id="XM">( X1 + X2 ) / 2</var>
<var id="YM">( Y1 + Y2 ) / 2</var>
</div>
<div class="problems">
<div id="find-midpoint">
<p class="question">What is the midpoint of the line segment from <code class="hint_blue">(<var>X1</var>, <var>Y1</var>)</code> to <code class="hint_green">(<var>X2</var>, <var>Y2</var>)</code>?</p>
<div class="graphie" id="graph">
graphInit({
range: 10,
scale: 20,
tickStep: 1,
labelStep: 1,
unityLabels: false,
labelFormat: function( s ) { return "\\small{" + s + "}"; },
axisArrows: "<->",
});
path([ [ X1, Y1 ], [ X2, Y2 ] ], {stroke:"#000000"});
style( point1Style );
label( [ X1, Y1 ], "(" + X1 + ", " + Y1 + ")",
getPos( [ X1,Y1 ], [ X2, Y2 ]) );
circle( [ X1, Y1 ], 0.15 );
style( point2Style );
label( [ X2, Y2 ], "(" + X2 + ", " + Y2 + ")",
getPos( [ X2,Y2 ], [ X1, Y1 ]) );
circle( [ X2, Y2 ], 0.15 );
</div>
<div class="solution" data-type="multiple">
(<span class="sol"><var>XM</var></span>, <span class="sol"><var>YM</var></span>)
</div>
<div class="hints">
<p>The <span class="hint_orange">x coordinate of the midpoint</span> is the average of the x coordinates <code class="hint_blue"><var>X1</var></code> and <code class="hint_green"><var>X2</var></code>.</p>
<div>
<p><code>x = \dfrac{1}{2}(<var>X1</var> + <var>X2</var>)</code></p>
<p><code>x = \dfrac{1}{2}(<var>X1 + X2</var>)</code></p>
<p><code class="hint_orange">x = <var>XM</var></code></p>
</div>
<span class="graphie" data-update="graph">
style( midPtStyle );
graph.vert = path( [ [ XM, -10], [ XM, 10] ] );
</span>
<p>The <span class="hint_orange">y coordinate of the midpoint</span> is the average of the y coordinates <code class="hint_blue"><var>Y1</var></code> and <code class="hint_green"><var>Y2</var></code>.</p>
<div>
<p><code>y = \dfrac{1}{2}(<var>Y1</var> + <var>Y2</var>)</code></p>
<p><code>y = \dfrac{1}{2}(<var>Y1 + Y2</var>)</code></p>
<p><code class="hint_orange">y = <var>YM</var></code></p>
</div>
<span class="graphie" data-update="graph">
graph.horiz = path( [ [ -10, YM], [ 10, YM ] ] );
</span>
<div>
<p>The midpoint is <code class="hint_orange">(<var>XM</var>, <var>YM</var>)</code>.</p>
<div class="graphie" data-update="graph">
circle( [ XM, YM ], 0.15 );
label( [ XM, YM ], "(" + XM + ", " + YM + ")",
getPos( [ XM, YM ], [ X1, Y1 ]) );
</div>
</div>
<div class="graphie" data-update="graph">
graph.vert.remove();
graph.horiz.remove();
</div>
</div>
</div>
<div id="find-point">
<p class="question">The point <code class="hint_orange" >(<var>XM</var>, <var>YM</var>)</code> is the midpoint of <code class="hint_blue">(<var>X1</var>, <var>Y1</var>)</code> and what point?</p>
<div class="graphie" id="graph">
graphInit({
range: 10,
scale: 20,
tickStep: 1,
labelStep: 1,
unityLabels: false,
labelFormat: function( s ) { return "\\small{" + s + "}"; },
axisArrows: "<->",
});
style( point1Style );
label( [ X1, Y1 ], "(" + X1 + ", " + Y1 + ")",
getPos( [ X1,Y1 ], [ XM, YM ]) );
graph.first = circle( [ X1, Y1 ], 0.15 );
style( midPtStyle );
label( [ XM, YM ], "(" + XM + ", " + YM + ")",
getPos( [ XM, YM ], [ X1, Y1 ]) );
graph.midpoint = circle( [ XM, YM ], 0.15 );
</div>
<div class="solution" data-type="multiple">
(<span class="sol"><var>X2</var></span>, <span class="sol"><var>Y2</var></span>)
</div>
<div class="hints">
<p>The average of the desired x coordinate and <code class="hint_blue"><var>X1</var></code> should be <code class="hint_orange"><var>XM</var></code>.</p>
<div>
<p><code>\dfrac{1}{2}(x + <var>X1</var>) = <var>XM</var></code></p>
<p>Solving for x:</p>
<p><code>x + <var>X1</var> = <var>(2 * XM)</var></code></p>
<p><code class="hint_green">x = <var>X2</var></code></p>
<span class="graphie" data-update="graph">
style( point2Style );
graph.vert = path( [ [ X2, -10], [ X2, 10] ] );
</span>
</div>
<p>The average of the desired y coordinate and <code class="hint_blue"><var>Y1</var></code> should be <code class="hint_orange"><var>YM</var></code>.</p>
<div>
<p><code>\dfrac{1}{2}(y + <var>Y1</var>) = <var>YM</var></code></p>
<p>Solving for y:</p>
<p><code>y + <var>Y1</var> = <var>(2 * YM)</var></code></p>
<p><code class="hint_green">y = <var>Y2</var></code></p>
<span class="graphie" data-update="graph">
graph.horiz = path( [ [ -10, Y2 ], [ 10, Y2 ] ] );
</span>
</div>
<div>
<p>The point <code class="hint_orange">(<var>XM</var>, <var>YM</var>)</code> is the midpoint of <code class="hint_blue">(<var>X1</var>, <var>Y1</var>)</code> and <code class="hint_green">(<var>X2</var>, <var>Y2</var>)</code>.
<span class="graphie" data-update="graph">
path([ [ X1, Y1 ], [ X2, Y2 ] ], {stroke:"#000000"});
circle( [ X2, Y2 ], 0.15 );
label( [ X2, Y2 ], "(" + X2 + ", " + Y2 + ")",
getPos( [ X2, Y2 ], [ XM, YM ]) );
graph.first.toFront();
graph.midpoint.toFront();
</span>
</div>
<div class="graphie" data-update="graph">
graph.vert.remove();
graph.horiz.remove();
</div>
</div>
</div>
</div>
</div>
</body>
</html>