SOLUTION: the sum of the measures of the interior angles of a polygon is between 2100 and 2400. how many sides does the polygon have? thanks..

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Question 135203: the sum of the measures of the interior angles of a polygon is between 2100 and 2400. how many sides does the polygon have? thanks..

Found 2 solutions by stanbon, Edwin McCravy:
Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
the sum of the measures of the interior angles of a polygon is between 2100 and 2400. how many sides does the polygon have? thanks..
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The number of sides is n where (n-2)*180 = sum of interior angles.
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INEQUALITY:
2100 <= (n-1)*180 <= 2400
35/3 <= n-1 <= 40/3
Add one along the line to get:
38/3 <= n <= 43/3
12 2/3 <= n <= 14 1/3
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since n is a whole number, n = 13 or 14
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Cheers,
Stan H.

Answer by Edwin McCravy(20060) About Me  (Show Source):
You can put this solution on YOUR website!
the sum of the measures of the interior angles of a polygon is between 2100 and 2400. how many sides does the polygon have? thanks.
The expression for the sum of the interior angles of
an n-sided polygon is:

%28n-2%29180°

2100+%3C=+%28n-2%29180%3C=2400

Divide all three sides by 60

2100%2F60+%3C=+%28%28n-2%29180%29%2F60%3C=2400%2F60

35+%3C=+%28n-2%293%3C=40

35+%3C=+3%28n-2%29%3C=40

35+%3C=+3n-6%3C=40

Add 6 to all three sides:

41+%3C=+3n%3C=46

Divide all three sides by 3

41%2F3+%3C=+%283n%29%2F3%3C=46%2F3

132%2F3+%3C=+n+%3C=+151%2F3

n must be an integer and the only
two integers between 132%2F3 and 151%2F3

are 14 and 15.

So the polygon could either

1. have 14 sides, with the sum of the interior angles being

%28n-2%29180°

%2814-2%29180°

%2812%29180°

2160°

OR

2. have 15 sides, with the sum of the interior angles being

%28n-2%29180°

%2815-2%29180°

%2813%29180°

2340°

So there are two solutions.  The number of sides is 14 or 15.

Edwin