construction for the 21-sided regular polygon?

Question

Is there a good construction for the 21-sided regular polygon using only a ruler and a compass? I no that this is not possible, but I mean a good aproximation construction. Is there any?

Answer 1

On a coordinate system draw a circle of radius 10.
Draw a line from the center of the circle through the point (10,3).
This line will intersect the circle at a point A. Now the arc from (10,0) to the point A should be very close to 1/21 of the entire circumference, so strech your compass from (10,10) to point A and then use that setting to draw additional chords starting at A.

Answer 2

So, to locate finished sum of the angles in a customary polygon, the equation is: one hundred eighty(n-2) = A the place n is the # of things, and A is the sum of all indoors angles if the interior attitude degree is a hundred and forty four, A could be 144n, so, one hundred eighty(n-2) = 144n 180n-360 = 144n 36n = 360 so, n = 10 so there are 10 factors in that polygon.