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<h1 class="center">Inverse Sine, Cosine, Tangent</h1>
<div class="def">
<p style="float:right; margin: 0 0 5px 10px;"><img src="images/adjacent-opposite-hypotenuse.svg" alt="Right-Angled Triangle" height="120" /></p><h3>Quick Answer: </h3><p>For a <a href="../right_angle_triangle.html">right-angled triangle</a>:</p>
<div style="clear:both"></div>
<p class="center"><img src="images/sin-sin-1.svg" alt="sin vs sin-1" /> </p>
<p>&nbsp;</p>
<p class="center">The <b>sine</b> function <span class="largest">sin</span> takes angle &theta; and gives the ratio <span class="intbl"> <em>opposite</em> <strong>hypotenuse </strong></span></p>
<p class="center">The <b>inverse sine</b> function <span class="largest">sin<sup>-1</sup></span> takes the ratio <span class="intbl"> <em>opposite</em><strong>hypotenuse </strong></span> and gives angle&nbsp;&theta;</p>
<p>And cosine and tangent follow a similar idea. </p>
</div>
<div class="example">
<h3>Example (lengths are only to one decimal place):</h3>
<p style="float:right; margin: 25px 0 25px 10px;"><img src="../geometry/images/triangle-28-40-49.gif" width="159" height="117" alt="triangle 2.8 4.0 4.9 has 35 degree angle" /></p>
<div class="tbl">
<div class="row"><span class="left"><b>sin(35&deg;)</b></span><span class="right">= Opposite / Hypotenuse </span></div>
<div class="row"><span class="left">&nbsp;</span><span class="right">= 2.8/4.9 </span></div>
<div class="row"><span class="left">&nbsp;</span><span class="right">= 0.57...</span></div>
<div class="row"><span class="left"></span></div>
<div class="row"><span class="left"><b>sin<sup>-1</sup>(Opposite / Hypotenuse)</b></span><span class="right">= sin<sup>-1</sup>(0.57...) </span></div>
<div class="row"><span class="left">&nbsp;</span><span class="right">= 35&deg;</span></div>
</div>
</div>
<h3>And now for the details:</h3>
<p><a href="../sine-cosine-tangent.html">Sine, Cosine and Tangent</a> are all based on a Right-Angled Triangle</p>
<p>They are very similar functions ...
so we will look at the <b>Sine Function</b> and then <b>Inverse Sine</b> to learn what it is all about.</p>
<h2>Sine Function</h2>
<p style="float:right; margin: 0 0 5px 10px;"><img src="images/adjacent-opposite-hypotenuse.svg" alt="triangle showing Opposite, Adjacent and Hypotenuse" /></p>
<p>The&nbsp;Sine&nbsp;of&nbsp;angle&nbsp;<b><i>&theta;</i></b>&nbsp;is:</p>
<ul>
<li>the <b>length of the side Opposite</b> angle <b><i>&theta;</i></b></li>
<li>divided by the <b>length of the Hypotenuse</b></li>
</ul>
<p align="left">Or more simply:</p>
<p align="center" class="larger">sin(<i>&theta;</i>) = Opposite / Hypotenuse</p>
<div class="example">
<h3>Example: What is the sine of 35&deg;?</h3>
<table width="100%" border="0">
<tr>
<td><img src="../geometry/images/triangle-28-40-49.gif" width="159" height="117" alt="triangle 2.8 4.0 4.9 has 35 degree angle" /></td>
<td><p>Using this triangle (lengths are only to one decimal place):</p>
<p class="center larger">sin(35&deg;) = Opposite / Hypotenuse <br>
= 2.8/4.9 <br>
= <b>0.57...</b></p></td>
</tr>
</table>
</div>
<p>The Sine Function can help us solve things like this:</p>
<div class="example">
<p style="float:right; margin: 0 0 5px 10px;"><img src="images/trig-2example2.gif" width="242" height="170" alt="trig ship example 30m at 39 degrees" /> </p>
<h3>Example: Use the <b>sine function</b> to find <b>&quot;d&quot;</b></h3>
<p>We know</p>
<ul>
<li>The angle the cable makes with the seabed is 39&deg; </li>
<li>The cable's length is 30 m. </li>
</ul>
<p> And we want to know &quot;d&quot; (the distance down).</p>
<div class="tbl">
<div class="row"><span class="left">Start with:</span><span class="right">sin 39&deg; = opposite/hypotenuse</span></div>
<div class="row"><span class="left">&nbsp;</span><span class="right"> sin 39&deg; = d/30</span></div>
<div class="row"><span class="left">Swap Sides:</span><span class="right">d/30 = sin 39&deg; </span></div>
<div class="row"><span class="left">Use a calculator to find sin 39&deg;:</span><span class="right"> d/30 = <span class="hilite">0.6293…</span></span></div>
<div class="row"><span class="left">Multiply both sides by 30:</span><span class="right">d = 0.6293… x 30 </span></div>
<div class="row"><span class="left">&nbsp;</span><span class="right">d = <b>18.88</b> to 2 decimal places</span></div>
</div>
<div class="indent50px"></div>
<p align="center" class="larger"> The depth &quot;d&quot; is <b>18.88 m</b></p>
</div>
<h2>Inverse Sine Function</h2>
<p>But sometimes it is the <b>angle</b> we need to find. </p>
<p>This is where &quot;Inverse Sine&quot; comes in. </p>
<p align="center" class="larger">It answers the question &quot;what <b>angle</b> has sine equal to opposite/hypotenuse?&quot;</p>
<p align="left">The symbol for inverse sine is <b>sin<sup>-1</sup></b>, or sometimes <b>arcsin</b>.</p>
<div class="example">
<p style="float:right; margin: 0 0 5px 10px;"><img src="images/trig-2example3.gif" width="242" height="170" alt="trig ship example 30m and 18.88m" /> </p>
<h3>Example: Find the angle <b>&quot;a&quot;</b></h3>
<p>We know</p>
<ul>
<li>The distance down is 18.88 m.</li>
<li>The cable's length is 30 m. </li>
</ul>
<p> And we want to know the angle &quot;a&quot;</p>
<p>&nbsp;</p>
<div class="tbl">
<div class="row"><span class="left">Start with:</span><span class="right">sin a&deg; = opposite/hypotenuse</span></div>
<div class="row"><span class="left">&nbsp;</span><span class="right"> sin a&deg; = 18.88/30</span></div>
<div class="row"><span class="left">Calculate 18.88/30:</span><span class="right">sin a&deg; = 0.6293...</span></div>
<p>What <b>angle</b> has sine equal to 0.6293...?<br />
The <b>Inverse Sine</b> will tell us.</p>
<div class="row"><span class="left">Inverse Sine:</span><span class="right">a&deg; = <b>sin<sup>&minus;1</sup></b>(0.6293...)</span></div>
<div class="row"><span class="left">Use a calculator to find <b>sin<sup>&minus;1</sup></b>(0.6293...):</span><span class="right">a&deg; = <b>39.0&deg;</b> (to 1 decimal place)</span></div>
</div>
<p align="center" class="larger"> The angle &quot;a&quot; is <b>39.0&deg;</b></p>
</div>
<h2>They Are Like Forward and Backwards!</h2>
<div align="center"><img src="images/sin-sin-1.svg" alt="sin vs sin-1" /></div>
<ul>
<li><span class="large">sin</span> takes an <b>angle</b> and gives us the <b>ratio</b> &quot;opposite/hypotenuse&quot;</li>
<li><span class="large">sin<sup>-1</sup></span> takes the <b>ratio</b> &quot;opposite/hypotenuse&quot; and gives us the <b>angle.</b></li>
</ul>
<div class="example">
<h3>Example:</h3>
<div class="tbl">
<div class="row"><span class="left">Sine Function:</span><span class="right">sin(<b>30&deg;</b>) = <b>0.5 &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;</b></span></div>
<div class="row"><span class="left">Inverse Sine:</span><span class="right">sin<sup>&minus;1</sup>(<b>0.5</b>) = <b>30&deg;</b></span></div>
</div>
</div>
<h2 align="left">Calculator</h2>
<table width="80%" border="0" align="center">
<tr>
<td><img src="images/calculator-sin-cos-tan.jpg" alt="calculator-sin-cos-tan" width="118" height="75" /></td>
<td>On the calculator you press one of the following (depending on your brand of calculator):
either '2ndF sin' or 'shift sin'.</td>
</tr>
</table>
<p align="center" class="center80">On your calculator, try using <span class="larger">sin</span> and then <span class="larger">sin<sup>-1</sup></span> to see what happens</p>
<h2 align="left">More Than One Angle!</h2>
<p align="left">Inverse Sine <b>only shows you one angle</b> ... but there are more angles that could work.</p>
<div class="example">
<h3 align="left">Example: Here are two angles where opposite/hypotenuse = 0.5</h3>
<p align="center"><br />
<img src="images/trig-inverse-sin-cos-tan1.gif" width="247" height="79" alt="triangle at 30 and 150 degrees" /></p>
</div>
<p align="left">In fact there are <b>infinitely many angles</b>, because you can keep adding (or subtracting) 360&deg;:</p>
<p align="center"><img src="images/trig-inverse-sin-cos-tan2.svg" alt="sine crosses 0.5 at 30,150,390, etc" style="max-width:100%" /></p>
<p align="left">Remember this, because there are times when you actually need one of the other angles!</p>
<h2 align="left">Summary</h2>
<p style="float:right; margin: 0 0 5px 10px;"><img src="images/adjacent-opposite-hypotenuse.svg" alt="Right-Angled Triangle" height="120" /></p>
<p>The Sine of angle <b><i>&theta;</i></b> is:</p>
<p align="center" class="larger">sin(<i>&theta;</i>) = Opposite / Hypotenuse</p>
<p>And Inverse Sine is :</p>
<p align="center" class="larger">sin<sup>-1</sup> (Opposite / Hypotenuse) = <i>&theta; </i></p>
<p>&nbsp;</p>
<h2>What About &quot;cos&quot; and &quot;tan&quot; ... ?</h2>
<p>Exactly the same idea, but different side ratios.</p>
<h4>Cosine</h4>
<p style="float:right; margin: 0 0 5px 10px;"><img src="images/adjacent-opposite-hypotenuse.svg" alt="Right-Angled Triangle" height="120" /></p>
<p>The Cosine of angle <b><i>&theta;</i></b> is:</p>
<p align="center" class="larger">cos(<i>&theta;</i>) = Adjacent / Hypotenuse</p>
<p>And Inverse Cosine is :</p>
<p align="center" class="larger">cos<sup>-1</sup> (Adjacent / Hypotenuse) = <i>&theta; </i></p>
<div class="example">
<p style="float:right; margin: 0 0 5px 10px;"><img src="images/trig-example2.gif" width="194" height="124" style="float:left; margin: 10px;" alt="trig example" /></p>
<h3>Example: Find the size of angle a&deg;</h3>
<p>cos a&deg; = Adjacent / Hypotenuse</p>
<p>cos a&deg; = 6,750/8,100 = 0.8333...</p>
<p>a&deg; = <b>cos<sup>-1</sup></b> (0.8333...) = <b>33.6&deg;</b> (to 1 decimal place)</p>
</div>
<h4>Tangent</h4>
<p style="float:right; margin: 0 0 5px 10px;"><img src="images/adjacent-opposite-hypotenuse.svg" alt="Right-Angled Triangle" height="120" /></p>
<p>The Tangent of angle <b><i>&theta;</i></b> is:</p>
<p align="center" class="larger">tan(<i>&theta;</i>) = Opposite / Adjacent</p>
<p>So Inverse Tangent is :</p>
<p align="center" class="larger">tan<sup>-1</sup> (Opposite / Adjacent) = <i>&theta;</i></p>
<div class="example">
<p style="float:right; margin: 0 0 5px 10px;"><img src="images/trig-example1.gif" width="220" height="160" alt="trig example" /> </p>
<h3>Example: Find the size of angle x&deg;</h3>
<p>tan x&deg; = Opposite / Adjacent </p>
<p>tan x&deg; = 300/400 = 0.75</p>
<p>x&deg; = <b>tan<sup>-1</sup></b> (0.75) = <b>36.9&deg;</b> (correct to 1 decimal place)</p>
</div>
<p>&nbsp;</p>
<h2>Other Names</h2>
<p class="words">Sometimes sin<sup>-1</sup> is called <b>asin</b> or <b>arcsin</b><br />
Likewise cos<sup>-1</sup> is called <b>acos</b> or <b>arccos</b><br />
And tan<sup>-1</sup> is called <b>atan</b> or <b>arctan</b></p>
<div class="example">
<h3>Examples:</h3>
<ul>
<li><b>arcsin(y)</b> is the same as <b>sin<sup>-1</sup>(y) </b><br />
</li>
<li><b>atan(&theta;)</b> is the same as <b>tan<sup>-1</sup>(&theta;)</b><br />
</li>
<li>etc.</li>
</ul>
</div>
<h2>The Graphs</h2>
<p>And lastly, here are the graphs of Sine, Inverse Sine, Cosine and Inverse Cosine:</p>
<div class="boxa" style="width: 395px;"><span class="boxa" style="width: 395px;"><img src="images/sine-graph.svg" alt="sine graph" /></span><br />
<span class="larger">Sine</span></div>
<div class="boxa" style="width: 195px;"><span class="boxa" style="width: 195px;"><img src="images/inverse-sine-graph.svg" alt="inverse sine graph" /></span><br />
<span class="larger">Inverse Sine</span></div>
<div class="boxa" style="width: 395px;"><span class="boxa" style="width: 395px;"><img src="images/cosine-graph.svg" alt="cosine graph" /></span><br />
<span class="larger">Cosine</span></div>
<div class="boxa" style="width: 195px;"><span class="boxa" style="width: 195px;"><img src="images/inverse-cosine-graph.svg" alt="inverse cosine graph" /></span><br />
<span class="larger">Inverse Cosine</span></div>
<p>Did you notice anything about the graphs? </p>
<ul>
<li>They look similar somehow, right?</li>
<li>But the Inverse Sine and Inverse Cosine don't &quot;go on forever&quot; like Sine and Cosine do ...</li>
</ul>
<div class="center80">
<p>Let us look at the example of Cosine. </p>
<p>Here is <b>Cosine</b> and <b>Inverse Cosine</b> plotted on the same graph:</p>
<p align="center"><img src="images/cosine-mirror-graph.svg" alt="cosine mirror graph" /><br>
<span class="larger">Cosine and Inverse Cosine </span></p>
<p>They are mirror images (about the diagonal)</p>
<p>But why does Inverse Cosine get chopped off at top and bottom (the dots are not really part of the function) ... ? </p>
<p class="center large">Because <a href="../sets/function.html">to be a function</a> it can only give <b>one answer</b> <br>
when we ask <i>&quot;what is cos<sup>-1</sup>(x) ?&quot;</i> </p>
<h3>One Answer or Infinitely Many Answers</h3>
<p>But we saw earlier that there are <b>infinitely many answers</b>, and the dotted line on the graph shows this.</p>
<p>So yes there <b>are</b> infinitely many answers ...</p>
<p>... but imagine you type <span class="hilite">0.5</span> into your calculator, press <span class="hilite">cos<sup>-1</sup></span> and it gives you a never ending list of possible answers ... </p>
<p align="center" class="larger">So we have this rule that <b>a function can only give one answer</b>.</p>
<p>So, by chopping it off like that we get just one answer, but <b>we should remember that there could be other answers</b>.</p>
</div>
<h2>Tangent and Inverse Tangent</h2>
<p>And here is the tangent function and inverse tangent. Can you see how they are mirror images (about the diagonal) ...? </p>
<div class="boxa" style="width: 395px;"><span class="boxa" style="width: 395px;"><img src="images/tangent-graph.svg" alt="tangent graph" /></span><span class="larger"><br>
Tangent</span></div>
<div class="boxa" style="width: 305px;"><span class="boxa" style="width: 305px;"><img src="images/inverse-tangent-graph.svg" alt="inverse tangent graph" /></span><span class="larger"><br />
Inverse Tangent</span></div>
<p>&nbsp;</p>
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