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In a certain regular polygon, the measure of each interior angle is four times the measure of each exterior angle. Find the number of sides in this regular polygon.

 Jun 19, 2018
 #1
avatar+2446 
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The interior angle of a regular polygon can be determined with the following formula:

 

180(n2)n where n represents the number of sides the polygon has

 

The measure of each exterior angle of a regular polygon can be determined using the following formula:

 

360n where n represents the number of sides the polygon has

 

According to the problem, "the measure of each interior angle is four times the measure of each exterior angle," so we can create an equation for this like the following:

 

180(n2)n=4(360n) Simplify both sides of the equation.
180n360n=1440n Because the denominators are equal, simply set the numerators equal to each other and solve. 
180n360=1440 Add 360 to both sides.
180n=1800 Divide by 180
n=10 sides  
   
 Jun 20, 2018
 #2
avatar+49 
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I like the second way better.

 x+4x=180. 5x=180. x=36.

Then using knowledge that the number of sides of a regular polygon is equal to 360/exterior angle measure, we see that 360/36=10, so there are 10 sides

 Jun 20, 2018

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