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![Online Geometry](h_triangle_center_910.jpg)
Geometry: Incenter, Incircle, Inradius of a triangle, Theorems
and Problems.
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![Incenter, Incircle, Index](incenter_incircle_17.jpg) |
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![Circle, Angle, Incenter, Isosceles triangle](../problem/p439_circle_angle_1.jpg) |
Proposed Problem 439.
Isosceles triangle, Cevian, Incenter, Angles, Circle. |
![Triangle, CIrcle, Incircle, Inradius](../problem/p435_circle_radius_1.jpg) |
Proposed Problem 435.
Triangle, Incircle, Inradius, Incenter, Congruent circles, tangent,
Measurement. |
![Triangle, Incircle, Excircle, Inradius, Exradius](../problem/p419_triangle_incircle_17.jpg) |
Proposed Problem 419.
Triangle, Cevian, Incircle, Excircle, Inradius, Exradius |
![Triangle, Incircle, Inradius, Tangent](../problem/p418_triangle_incircle_17.jpg) |
Proposed Problem 418.
Triangle, Incircle, Inradius, Equal Tangent circles, Radius. |
![Triangle, Incenter, Parallel to a side](../problem/p378_triangle_incenter_17.jpg) |
Proposed Problem 378.
Triangle, Incenter, Parallel to a side, Angle, Congruence. |
![Tiangle, Incenter, Angle](../problem/p374_triangle_incenter_17.jpg) |
Proposed Problem 374.
Triangle, Incenter, Internal Angle Bisectors. |
![Triangle, Circumcenter, Incenter, Excenter, Collinear](../problem/p320_triangle_incenter_17.jpg) |
Proposed Problem 320.
Triangle, Circumcircle, Incenter, Excenter, Collinear points. |
![](../geometry/sangaku_cyclic_quad_170_2.jpg) |
Sangaku Geometry Theorem: Cyclic Quadrilateral.
Incenters, Incircles, Inradii, Rectangle. |
![](../geometry/sangaku_japanese_170_1.jpg) |
Sangaku Problem (An Old Japanese Theorem).
Incenters, Incircles, Inradii, Carnot's theorem. |
![](../equal_incircles_170.jpg)
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Equal Incircles Theorem: Triangles,
cevians, circles. |
![](../circle/adams_circle_theorem_170.jpg) |
Adams' Circle
Theorem
Concentric to the Incircle. |
![](spieker_center_170.jpg) |
Spieker Center
Incenter of the medial triangle. |
![](../heron/heron__proof_170x100.jpg) |
Heron's Formula.
Key facts and
a purely geometric
step-by-step proof.
Incenter, Incircle, Excenter.
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![](../semiperimeter_incircle170.jpg) |
Semiperimeter and incircle of a triangle. |
![](../semiperimeter_in_exc170.jpg) |
Semiperimeter, incircle and excircles of a triangle.
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![Gergonne Point Theorem](../gergonne170x100.jpg) |
Gergonne Point Theorem.
Incenter, Incircle, Concurrency. Interactive proof with animation.
Key concept: Ceva's Theorem.
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![](../Bevan170.jpg) |
The Bevan Point The
circumcenter of the excentral triangle.
Illustration with animation.
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![Gergonne Line](../geometry/gergonne_line_17.jpg) |
Interactive Gergonne Line and Nobbs Points.
Dynamic Geometry.
Step-by-Step construction, Manipulation, and animation.
Incenter and the points of contact of the incircle. |
![Interactive Geometry](../geometry/triangle_incircle_perpendic.jpg) |
Triangle: Incircle, Perpendicular, Angle Bisector.
Dynamic Geometry.
Step-by-Step construction, Manipulation, and animation.
Prove proposition. |
![](../pythagoras/right_triangle_facts_170.jpg) |
Right Triangles, Formulas and Facts
Pythagorean theorem, Similarity, Geometric mean,
hypotenuse, cathetus (legs), semiperimeter, altitude, median,
similar shapes areas, centers, orthocenter, incenter,
incircle, centroid, circumcenter, radius, inradius. |
![](feuerbach_point_facts_170.jpg) |
Feuerbach
Point Facts
Incenter, Incircle, Nine point circle, Circumcircle. |
![](feuerbach_theorem_acute_170.jpg) |
Feuerbach
Theorem, Acute Triangle illustration
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![](feuerbach_theorem_obtuse_17.jpg) |
Feuerbach
Theorem, Obtuse Triangle illustration
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![](feuerbach_theorem_right_170.jpg) |
Feuerbach
Theorem, Right Triangle illustration
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![](feuerbach_170.jpg) |
Feuerbach Theorem
One of the most striking theorems in triangle geometry. |
![Elearning 279: Tangent circles](../problem/p279_tangent_circles_17.jpg) |
Proposed Problem 279 Incircle.
Tangent Circles, Common External Tangent, Chords, Inradius. |
![Sagitta Problem](../problem/p275_right_triangle_sagitta.jpg) |
Proposed Problem 275.
Right Triangle, Incenter, Circumcircle, Sagitta, Inradius. |
![Elearning 260: Problem about equilateral triangle](../problem/p260_equilateral_triangle_1.jpg) |
Proposed Problem 260.
Equilateral Triangle, Incircle, Tangency Points, Vertices, Distances,
Squares.
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![Elearning 259: Equilateral triangle, Incircle](../problem/p259_equilateral_triangle_1.jpg) |
Proposed Problem 259.
Equilateral Triangle, Incircle, Tangency Points, Side, Distances,
Squares.
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![Elearning 258: Equilateral triangle, Incircle](../problem/p258_equilateral_triangle_1.jpg) |
Proposed Problem 258 Incircle.
Equilateral Triangle, Circumcircle, Point, Vertices, Side, Distances,
Squares.
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![Elearning: Napoleon Theorem III](../problem/p248_napoleon_theorem_17.jpg) |
Proposed Problem 248.
Napoleon's Theorem III. Inner and outer Napoleon triangles, Area.
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