Math help please? Need this clarified?

Test Preparation SAT Preparation
1

<p>How would I be able to find the radius of a circle if I had to find the area of the sector? I understand the sector formula, but I don't understand how to find ''r''/the radius, since they don't usually provide it. Thanks.</p>

2

<p>What is the sector formula?</p>

3

<p>Ratios</p>

<p>@Iceqube Sarea=0.5<em>r^2</em>angle
Slength=r*angle</p>

4

<p>Oh sorry…by ‘‘sector formula’’, I mean:</p>

<p>(n degrees/360 degrees)*2 pie r</p>

<p>…How am I supposed to find ‘‘r’’?</p>

5

<p>The radius is usually given, if they want a quantity. But I don’t really understand what you’re asking. Could you give us a test question as an example?</p>

6

<p>You should be able to solve for r if r is the only unknown in an equation.</p>

<p>As Clepsydra said, you could post the question here.</p>

7

<p>I mean, in this kind of a situation:</p>

<p><a href=“http://i252.■■■■■■■■■■■■■■■/albums/hh17/xxEliza321xx/Photoon8-28-11at1054PM.jpg[/url]”>http://i252.■■■■■■■■■■■■■■■/albums/hh17/xxEliza321xx/Photoon8-28-11at1054PM.jpg&lt;/a&gt;&lt;/p&gt;

<p>Chung doesn’t give me the value of ‘‘r’’ here.</p>

8

<p>Given: arclength of sector = 4; sector has angle of 45 degrees
Problem: Find the area of the sector</p>

<p>Solution: arclength of sector = (45 degrees/360 degrees)<em>2 pi r = 4
r = 16/ pi [use algebra]
Plug in r = 16/ pi into the formula for area of the a sector
area of sector = (45 degrees/360 degrees)</em> pi r^2</p>

<p>Answer: D) 32/ pi</p>

9

<p>There you don’t need the area of a sector. You need the length of an arc. That is L(length)=(angle/360)C where C is the circumference of the circle. You have L and the angle so you can solve for C the circumference then the radius from there</p>

10

<p>@knowthestuff, what do you mean by ‘‘use algebra’’? What kind of equation do I set up?</p>

11

<p>From the formula for the arclength and the given information, we can state:</p>

<p>(45 degrees/360 degrees)<em>2 pi r = 4
90/360 * pi * r = 4
1/4</em>pi * r = 4</p>

<p>Multiply both sides by 4/ pi</p>

<p>r = 16 / pi</p>

12

<p>Since the formulas both use radians, convert to radians by multiplying the number of degrees by pi/360. So 45 degrees would be pi/4. </p>

<p>You know the arc length formula: arc length = radius * angle (in radians). Now that you have both the angle in radians and the arc length (given as 4), you can solve for the radius. </p>

<p>Plug the radius and angle into the sector area formula.</p>

<p>Worked out on paper:
<a href=“http://i2.■■■■■■■■■■■■■■■/albums/y32/sando__aqua12/DSCN0587.jpg[/url]”>http://i2.■■■■■■■■■■■■■■■/albums/y32/sando__aqua12/DSCN0587.jpg&lt;/a&gt;&lt;/p&gt;

13

<p>Ok thank you :)</p>