SOLUTION: In paragraph form, prove that there is no regular polygon with each interior angle measuring 145° (Prove using indirect proof as well)

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Question 1106736: In paragraph form, prove that there is no regular polygon with
each interior angle measuring 145°
(Prove using indirect proof as well)

Answer by Edwin McCravy(20064) About Me  (Show Source):
You can put this solution on YOUR website!
The formula for the common measure of each of the
interior angles of a regular polygon with n-sides 
is 145°.

%28%28n-2%29%2A%22180%B0%22%29%2Fn

We set that equal to 145°:

%28%28n-2%29%2A%22180%B0%22%29%2Fn%22%22=%22%22%22145%B0%22

Multiply both sides by n

%28n-2%29%2A%22180%B0%22%22%22=%22%22%22145%B0%22n

%22180%B0%22%28n-2%29%22%22=%22%22%22145%B0%22n

%22180%B0%22%2An-%22360%B0%22%22%22=%22%22%22145%B0%22n

Add 360° to both sides:

%22180%B0%22%2An%22%22=%22%22%22145%B0%22n%2B%22360%B0%22

Subtract 145°n to both sides

%2235%B0%22%2An%22%22=%22%22%22360%B0%22

Divide both sides by 35°

%2235%B0%22%2An%22%22=%22%22%22360%B0%22


n%22%22=%22%22%22360%B0%22%2F%2235%B0%22

Cancel the degrees:

n%22%22=%22%22360%2F35

n%22%22=%22%2272%2F7

n%22%22=%22%2210%262%2F7

A regular polygon can only have a integer
for its number of sides.

Proved!
------------------------

Indirect proof:

Assume that there is a regular polygon such that each of 
its interior angles of a regular polygon with n-sides is.

The formula for the common measure of each of the
interior angles of a regular polygon with n-sides 
is 145°.

%28%28n-2%29%2A%22180%B0%22%29%2Fn

We set that equal to 145°:

%28%28n-2%29%2A%22180%B0%22%29%2Fn%22%22=%22%22%22145%B0%22

Multiply both sides by n

%28n-2%29%2A%22180%B0%22%22%22=%22%22%22145%B0%22n

%22180%B0%22%28n-2%29%22%22=%22%22%22145%B0%22n

%22180%B0%22%2An-%22360%B0%22%22%22=%22%22%22145%B0%22n

Add 360° to both sides:

%22180%B0%22%2An%22%22=%22%22%22145%B0%22n%2B%22360%B0%22

Subtract 145°n to both sides

%2235%B0%22%2An%22%22=%22%22%22360%B0%22

Divide both sides by 35°

%2235%B0%22%2An%22%22=%22%22%22360%B0%22


n%22%22=%22%22%22360%B0%22%2F%2235%B0%22

Cancel the degrees:

n%22%22=%22%22360%2F35

n%22%22=%22%2272%2F7

n%22%22=%22%2210%262%2F7

n is not an integer, so there is no such regular 
polygon.  This contradicts the assumption that 
there is such a regular polygon.

Proved!

Edwin