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Some illustrations of theorems in Geometry
The square on the hypotenuse of a right triangle is equal to the sum
of the squares on the other two sides.
The medians of a triangle are concurrent at the centroid.
The altitudes of a triangle are concurrent at the orthocentre.
The internal bisectors of the angles of a triangle are concurrent at
the centre of the incircle.
The perpendicular bisectors of the sides of a triangle are
concurrent at the centre of the circumcircle.
The Simson Line
The Nine-Point Circle
The Euler Line
The "outer" internal angle trisectors of a triangle intersect to
form an equilateral triangle.