

Online Geometry: Triangle Centers,
Theorems and Problems Index, Page 3

Triangle Centers  Table of
Content 3




Proposed Problem 156. Triangle,
Circumradius, Exradius, Chord, Secant line. 

Proposed Problem 155. Euler's
Theorem: Distance from the Incenter to the Circumcenter. 

Proposed Problem 154. Triangle,
Inradius, Circumradius, Chord. 

Proposed Problem 145. Four
Triangles, Incircle, Tangent and Parallel to Side, Incenters,
Circumcenters. 

Proposed Problem 144. Four
Triangles, Incircle, Tangent and Parallel to Side, Inradii. 

Proposed Problem 143. Four
Triangles, Incircle, Tangent and Parallel to Side, Circumradii. 

Proposed Problem 142. Four
Triangles, Incircle, Tangent and Parallel to Side, Areas. 

Proposed Problem 141. Triangle,
Incircle, Tangent , Parallel, Perimeters. 

Proposed Problem 140. Triangle,
Excircle, Tangent, Semiperimeter. 

Proposed Problem 139. Triangle
Area, Orthic Triangle, Semiperimeter, Circumradius. 

Proposed Problem 138. Nagel's
Theorem, Orthic Triangle, Altitudes, Circumradius, Perpendicular.


Proposed Problem 137.
Orthic Triangle, Altitudes, Perpendicular, Incircle, Collinear Points,
Parallelogram. 

Proposed Problem 136. Orthic
Triangle, Altitudes, Perpendicular, Concyclic Points. 

Proposed Problem 135. Orthic
Triangle, Altitudes, Perpendicular, Parallel 

Proposed Problem 134. Orthic
Triangle, Altitudes, Angle Bisectors, Orthocenter, Incenter. 

Interactive Gergonne Line and Nobbs Points.
Dynamic Geometry.
StepbyStep construction, Manipulation, and animation. 

Triangle, Medians, Six Circumcenters Concyclic.
Dynamic Geometry.
StepbyStep construction, Manipulation, and animation.
Prove proposition. 

Triangle: Incircle, Perpendicular, Angle Bisector.
Dynamic Geometry.
StepbyStep construction, Manipulation, and animation.
Prove proposition. 

Proposed Problem 133. Triangle,
Angle Bisectors, Collinear Points.


Proposed Problem 132.
Triangle, 60 degree, Orthocenter, Congruence, Midpoint.


Triangle with the
bisectors of the exterior angles. Collinearity. Key concept:
Menelaus Theorem.


Proposed Problem 128. Incenter of
a Triangle, Angle Bisectors, Sum of Ratios.


Proposed Problem 127. Centroid
and Incenter of a Triangle, Parallel, Proportions.


Proposed Problem 126. Incenter of
Triangle, Angle Bisector, Proportions.


Proposed Problem 120. Area
of triangle, incenter, excircles, tangent.


Proposed Problem 119. Area
of triangle, incenter, excircle, tangent.


Proposed Problem 118. Area
of triangle, incenter, excenter, tangent.


Proposed Problem 117. Area
of triangle, incenter, excircles, tangent.


Proposed Problem 116. Area
of triangle, excircles, tangent.


Proposed Problem 115. Area
of triangle, excircles, tangent.


Proposed Problem 114. Area of
triangle, incircle, excircle.


Proposed Problem 113. Area of
triangle, incircle, excircle.


Complete Quadrilateral: OrtholineSteiner Line.
Using TracenPoche Dynamic Software
StepbyStep construction, Manipulation, and animation 

Proposed Problem 96. Similar
Triangles, Incenters, Parallelogram. 

Proposed Problem 95. Similar
Triangles, Inradii, Parallel. 

Proposed Problem 94. Similar
Triangles, Circumcircles, Circumradii. 

Proposed Problem 93. Similar
Triangles, Circumcircles, Parallelogram. 

Proposed Problem 92. Similar
Triangles, Circumcircles, Circumradii, Parallel. 

Intouch and Extouch Triangles. Puzzle cut: 20 Piece Classic
Based on Proposed Problem 86. 

Proposed Problem 86. Intouch and
Extouch Triangles, Areas. 

Contact Triangles. Puzzle cut: 22 Piece Polygons
Based on Proposed Problem 85. 

Proposed Problem 85. Contact
Triangles Areas, Incircle, Excircle. 

Proposed Problem 84. Contact
Triangles Areas, Incircle, Excircle, Inradius, Exradius. 

Proposed Problem 83. Area of the
Excircle Contact Triangle, exradius, circumradius. 

Proposed Problem 82. Area of the
Contact Triangle, inradius, circumradius. 

Proposed Problem 81. Area of a
triangle, side, inradius, circumradius. 

Proposed Problem 80. Area of a
triangle, side, incircle, inradius. 
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