LE1 add doenets for vector operations (#908)

* adding vectors visualization

* add scalar multiplication doenet

Author: StevenClontz

source/linear-algebra/source/01-LE/01.ptx

@@ -234,6 +234,22 @@ Following are some examples of addition and scalar multiplication in <m>\mathbb
 </me>
         </p>
     </example>
+    <figure xml:id="figure-le1-add-vectors">
+        <caption>Visualization of adding vectors</caption>
+        <interactive label="LE1-interactive-add-vectors" platform="doenetml" width="100%">
+          <slate surface="doenetml">
+            <xi:include parse="text" href="doenet/LE1-add-vectors.xml"/>
+          </slate>
+        </interactive>
+    </figure>
+    <figure xml:id="figure-le1-scalar-mult">
+        <caption>Visualization of adding vectors</caption>
+        <interactive label="LE1-interactive-scalar-mult" platform="doenetml" width="100%">
+          <slate surface="doenetml">
+            <xi:include parse="text" href="doenet/LE1-scalar-mult.xml"/>
+          </slate>
+        </interactive>
+    </figure>
     <definition>
         <statement>
             <p>

source/linear-algebra/source/01-LE/doenet/LE1-add-vectors.xml

@@ -0,0 +1,29 @@
+<p>
+  Move the vectors to visualize their sum.
+</p>
+<setup><math name="vw" simplify>$v+$w</math></setup>
+<graph xmin="-1" ymin="-1" xmax="8" ymax="8">
+<point name="v" styleNumber="1" >
+    (3,2)
+    <label><m>\vec v=\left[\begin{array}{c} $v.x \\ $v.y\end{array}\right]</m></label>
+    <constraints>
+    <constrainToGrid dx="0.5" dy="0.5"/>
+    </constraints>
+</point>
+<point name="w" styleNumber="2" >
+    (1,4)
+    <label><m>\vec w=\left[\begin{array}{c} $w.x \\ $w.y\end{array}\right]</m></label>
+    <constraints>
+    <constrainToGrid dx="0.5" dy="0.5"/>
+    </constraints>
+</point>
+<point draggable="false" styleNumber="3" >
+    $v+$w
+    <label><m>\vec v+\vec w=\left[\begin{array}{c} $v.x+$w.x \\ $v.y+$w.y\end{array}\right]
+    =\left[\begin{array}{c} $vw.x \\ $vw.y \end{array}\right]</m></label>
+</point>
+<lineSegment draggable="false" styleNumber="1" endpoints="(0,0) $v"/>
+<lineSegment draggable="false" styleNumber="2" endpoints="(0,0) $w"/>
+<lineSegment draggable="false" styleNumber="3" endpoints="(0,0) $v+$w"/>
+<polygon draggable="false" styleNumber="6" vertices="(0,0) $w $v+$w $v"/>
+</graph>

source/linear-algebra/source/01-LE/doenet/LE1-scalar-mult.xml

@@ -0,0 +1,21 @@
+<p>
+  Move the vector and slider to visualize a scalar multiple of a vector.
+</p>
+<slider name="c" step="0.5" displayDigits="true" from="-5" to="5" initialValue="2"/>
+<setup><math name="cv" simplify="true">$c*$v</math></setup>
+<graph xmin="-10" ymin="-10" xmax="10" ymax="10">
+<point name="v" styleNumber="1" >
+    (1,2)
+    <label><m>\vec v=\left[\begin{array}{c} $v.x \\ $v.y\end{array}\right]</m></label>
+    <constraints>
+    <constrainToGrid dx="0.5" dy="0.5"/>
+    </constraints>
+</point>
+<point draggable="false" styleNumber="2" >
+    $cv
+    <label><m>c\vec v=\left[\begin{array}{c} $c($v.x) \\ $c($v.y)\end{array}\right]
+    =\left[\begin{array}{c} $cv.x \\ $cv.y \end{array}\right]</m></label>
+</point>
+<lineSegment draggable="false" styleNumber="1" endpoints="(0,0) $v"/>
+<lineSegment draggable="false" styleNumber="2" endpoints="(0,0) $cv"/>
+</graph>