SOLUTION: You are given the measure of each interior angle of a regular n-gon. Find the value of n. 12.) 128 4/7 degrees i know you must use the formula n x (n-2) x 180

Algebra ->  Formulas -> SOLUTION: You are given the measure of each interior angle of a regular n-gon. Find the value of n. 12.) 128 4/7 degrees i know you must use the formula n x (n-2) x 180       Log On


   



Question 133460: You are given the measure of each interior angle of a regular n-gon. Find the value of n.
12.) 128 4/7 degrees

i know you must use the formula
n x (n-2) x 180
---------------
n

but Im not sure what to do from here...

Answer by solver91311(24713) About Me  (Show Source):
You can put this solution on YOUR website!
Actually, you have an extra factor of n in the numerator of your formula. The formula for the measure of the interior angles of a regular n-sided polygon is:

%28%28n-2%29%2A180%29%2Fn.

Since you are given that the measure of the interior angle of your regular polygon is 128 4/7 degrees, you need to set your formula equal to this measure and then solve for n. Just as a sanity check, since the denominator of the fraction in the angular measure is 7, I expect that the number of sides will turn out to be 7 or some multiple of 7.

%28%28n-2%29%2A180%29%2Fn=128%2B4%2F7

Multiply both sides by n:
%28%28n-2%29%2A180%29=n%28128%2B4%2F7%29 (I added the whole number part of the angle measure and the fractional part because this formula system won't render mixed numbers)

Distribute:
180n-360=128n%2B4n%2F7

Put the variable terms on the left, and the constants on the right:
180n-128n-4n%2F7=360

Rather than converting everything to fractions, just multiply both sides by the denominator of 7:
1260n-896n-4n=2520

360n=2520

n=7, as suspected.