Copyright ©2005 by Paul Niquette, all rights reserved. 
he
figure on the right is a circle with radius a.
Its
equation is x^{2}
+ y^{2}
= a^{2}.
Point P is located along the circumference at some angle Φ measured counterclockwise from the xaxis. Point Q is located exactly π radians (180 degrees) beyond P. By inspection, we ascertain that PQ = 2a
and
PQ is the longest line segment that will fit within
the figure. The
angle Φ
can
be assigned any value from 0 to 2π
radians (360 degrees) and PQ will always fit within
the figure.

