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they ???? a symmetric trapezoid

送交者: InCaseYouLikeIt 2008年4月11日08:34:30 于 [灵机一动]http://www.bbsland.com
回 答: 简单球面几何问题 由 羽球飞 于 2008年4月04日09:21:34:

 


???? a plane passing through the north and south poles with its longitude right between J1 and J2. Then the line passing through (J1, W1) and (J2,W1) is perpendicular to the plane. The line passing through (J1, W2) and (J2, W2) is also perpendicular to the plane. Thus the two lines are parallel and therefore the four points lie in a plane.

Then we see that the four points ???? a symmetric trapezoid and hence they lie in a circle.

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