单词	nine-point circle
释义	nine-point circle For a triangle, let M1, M2, M3 denote the midpoints of the three sides. These three points define a circle known as Feuerbach's circle or the nine-point circle. It gets its name because it passes through six further points of note. It passes through A1, A2, A3, the three feet of the altitudes. The altitudes meet at the orthocentre O, and Feuerbach's circle also passes through the midpoints of the line segments from the orthocentre to each vertex. The centre of the circle lies on the Euler line, halfway between the orthocentre and circumcentre. Further, Feuerbach's circle touches the incircle and the three excircles of the triangle. The nine points and circle
随便看	Fourier transform four squares theorem fourth root of unity Fq fractal fractal dimension fraction fractional part frame of reference framework Fredholm alternative Fredholm integral equation Freedman, Michael Hartley free group freely hinged free module Frege, (Friedrich Ludwig) Gottlob frequency frequency frequency analysis frequency distribution frequentist inference Freudenthal, Hans Frey's curve friction

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