3. challenge in obtuse triangle abc, bc is the longest side. ac is also a side of a 21-sided regular polygon. ab is also a
side of a 28-sided regular polygon. the 21-sided regular polygon and the 28-sided regular polygon have the same
center point p. find n if bc is a side of a n-sided regular polygon that has center point p.
(hint: sketch a circle with center p and place points a, b, and on the circle.)