Online Geometry: Area of a triangle, Theorems and Problems - Table of Content

Heron's Formula.
Key facts and a purely geometric step-by-step proof.
 

Area of a Right Triangle, Theorems and Problems.

Varignon and Wittenbauer parallelograms. Quadrilateral: midpoints and trisection points of the edges. Triangle areas.

Routh's Theorem - Index
Triangle, Cevians, Area, Ratio.
 

Marion Walter's Theorem and Related Topics: Index

Geometry Problem 880
Triangle, Midpoints, Sides, Perpendiculars, Hexagon, Area.

Geometry Problem 876
Equilateral Triangle, any Point, Perpendicular, Right Triangle Area, Sum of Areas.

Geometry Problem 860
Triangle, Three Medians, Parallel, Parallelogram, Area, Congruence.

Geometry Problem 854
Triangle, Parallel lines, Parallelogram, Areas, Similarity, Concurrent lines.

Geometry Problem 791
Regular Hexagon, Midpoints of Side and Diagonal, Equilateral Triangle, Area.

Geometry Problem 619
Triangle Area, 30 Degrees, Incircle, Incenter, Tangent.

Geometry Problem 618
Triangle Area, 60 Degrees, Incircle, Incenter, Tangent.

Geometry Problem 617
Right Triangle Area, Incircle, Incenter, Tangent, 90 Degrees.

Problem 579.
Quadrilateral, Diagonals, Triangles, Areas.

Problem 558.
Quadrilateral, Trisection, Sides, Wittenbauer Parallelogram, Area, Auxiliary Lines.

Problem 557.
Quadrilateral, Midpoints, Sides, Varignon Parallelogram, Area, Auxiliary Lines.

Problem 545.
Acute Triangle, Squares, Altitudes, Area, Measure.

Problem 540.
Right Triangle, Square, Parallel, Perpendicular, Dissection, Area, Pythagoras.

Problem 539.
Right Triangle, Square, Parallel, Perpendicular, Dissection, Area, Pythagoras.

Proposed Problem 433.
Quadrilateral, Triangle, Area, Proportion, Measurement, Similarity.

Proposed Problem 416.
Triangle, Cevians, Trisectors, Area.

Proposed Problem 401.
Area, Triangle, Angle bisector, Circumcircle, Perpendicular bisector, Congruence.

Proposed Problem 371.
Square, Inscribed circle, Triangle, Area.

Proposed Problem 364.
Obtuse triangle, Congruence, Circles, Diameter, Curvilinear triangle, Area.

Proposed Problem 360.
Area of a triangle, Curvilinear triangles, Circles, Diameters.

Proposed Problem 357.
Square, Exterior point, Triangles, Area.

Proposed Problem 356.
Square, Point inside, Triangles, Area.

Proposed Problem 322.
Square, Inscribed circle, Tangent, Triangle area.

Proposed Problem 273.
Triangle, Perpendiculars, Area of Squares.

Proposed Problem 252.
Rectangle, isosceles right triangle, square, area.

Proposed Problem 248.
Napoleon's Theorem III. Inner and outer Napoleon triangles areas.

Proposed Problem 225. Viviani's Theorem Extension, Regular Polygon, Apothem, Distance. Area of triangles. 

Proposed Problem 224. Viviani's theorem, Isosceles triangle, Altitude, Distances, Point on the extension of the base. Area of triangles.  

Proposed Problem 223. Viviani's theorem, Isosceles triangle, Altitude, Distances. Area of triangles.  

Proposed Problem 222. Viviani's theorem, Equilateral triangle, Exterior point, Distances. Area of triangles.  

Proposed Problem 221. Viviani's theorem, Equilateral triangle, Interior point, Distances. Area of triangles.  

Lune of Hippocrates Index. Area of a right triangle. 

Proposed Problem 212. 120 Degree Triangle, Equilateral triangles, Areas.

Proposed Problem 211. 60 Degree Triangle, Equilateral triangles, Areas.

Problem 206. Area of a Right Triangle, Inradius, and Exradius relative to the hypotenuse.  

Proposed Problem 205. Right Triangle Area, Exradii relatives to legs or catheti.  

Proposed Problem 197. Area of a Triangle, Side, Inradius, and Exradius.

Proposed Problem 196. Area of triangles, Inradius and Exradii Formula.

Proposed Problem 195. Area of a Triangle, Inradius, Exradii.  

Proposed Problem 194. Area of a Triangle, Semiperimeter, Exradius.

Proposed Problem 193. Area of a Triangle, Semiperimeter, Inradius.

Proposed Problem 192. Circle, Diameter, Chord, Perpendicular, Triangle, Area.

Proposed Problem 191. Triangle, Altitudes, Orthocenter, Squares, Areas.

Proposed Problem 180. Circles Tangent Externally, Common External Tangents, Triangle Areas.  

Proposed Problem 177. Parallelogram with Midpoints, Triangles, Areas.  

Proposed Problem 176. Quadrilateral with Midpoints, Triangles, Areas.  

Proposed Problem 174. Quadrilateral with Midpoints, Triangles, Areas.  

Proposed Problem 173. Quadrilateral with Midpoints, Triangles, Areas.  

Proposed Problem 172. Trapezoid, Midpoints, Quadrilaterals, Areas.  

Proposed Problem 171. Trapezoid, Midpoints, Triangles, Areas.  

Proposed Problem 170. Trapezoid, Midpoint, Triangle, Area.  

Proposed Problem 169. Parallelogram, Interior and Exterior Points, Diagonals, Pentagon, Triangles, Areas  

Proposed Problem 168. Parallelogram, Diagonal, Triangles, Pentagon, Areas.  

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