This is a weaker area inequality than the one in Corollary 2, which can be seen in
the following way. An inequality between the two radii of a bicentric quadrilateral
is R
p2r. 2 From this it follows that 4R2 8r2, and so
3r p4R2 + r2.
Hence, from Theorem 1, we have
K
r r +p4R2 + r2 4
3p4R2 + r2
so the expression in Corollary 2 gives a sharper upper bound for the area.
2References to several different proofs of this inequality are given at the end of [6], where we
provided a new proof of an extension to this inequality.
240 M. Josefsson
3. Construction of the maximal bicentric quadrilateral
Given two circles, one within the other, and assuming that a bicentric quadrilateral
exist inscribed in the larger circle and circumscribed around the smaller, then
among the infinitely many such quadrilaterals that are associated with these circles,
Corollary 2 states that the one with maximal area is a right kite. Since a kite
has a diagonal that is a line of symmetry, the construction of this is easy. Draw a
line through the two centers of the circles. It intersect the circumcircle at A and C.
Now all that is left is to construct tangents to the incircle through A. This is done by
constructing the midpoint M between the incenter I and A, and drawing the circle
with center M and radius MI according to [7]. This circle intersect the incircle at
E and F. Draw the tangents AE and AF extended to intersect the circumcircle at
B and D. Finally connect the points ABCD, which is the right kite with maximal
area of all bicentric quadrilaterals associated with the two circles having centers I
and O.
b
I
bO
b
A
b C
bM
F b
b
E
b D
b
B
Figure 2. Construction of the right kite ABCD
This is a weaker area inequality than the one in Corollary 2, which can be seen inthe following way. An inequality between the two radii of a bicentric quadrilateralis R p2r. 2 From this it follows that 4R2 8r2, and so3r p4R2 + r2.Hence, from Theorem 1, we haveKr r +p4R2 + r2 43p4R2 + r2so the expression in Corollary 2 gives a sharper upper bound for the area.2References to several different proofs of this inequality are given at the end of [6], where weprovided a new proof of an extension to this inequality.240 M. Josefsson3. Construction of the maximal bicentric quadrilateralGiven two circles, one within the other, and assuming that a bicentric quadrilateralexist inscribed in the larger circle and circumscribed around the smaller, thenamong the infinitely many such quadrilaterals that are associated with these circles,Corollary 2 states that the one with maximal area is a right kite. Since a kitehas a diagonal that is a line of symmetry, the construction of this is easy. Draw aline through the two centers of the circles. It intersect the circumcircle at A and C.Now all that is left is to construct tangents to the incircle through A. This is done byconstructing the midpoint M between the incenter I and A, and drawing the circlewith center M and radius MI according to [7]. This circle intersect the incircle atE and F. Draw the tangents AE and AF extended to intersect the circumcircle atB และ d ในที่สุด เชื่อมต่อจุด ABCD ซึ่งเป็นว่าวเหมาะกับสูงสุดquadrilaterals bicentric ทั้งหมดสัมพันธ์กับพื้นที่ของวงกลมสองที่มีศูนย์ผมและ obผมบ่อbAb Cองค์การสหประชาชาติF bbอีb DbBรูปที่ 2 ก่อสร้างของว่าวขวา ABCD
การแปล กรุณารอสักครู่..
