This paper presents a new method of drawing perspective shade and shadow in parallel rays, which makes use of plane trace and geometrical drawing method.

探讨了一种利用平面迹线和几何作图法，作无灭光线下透视阴影的新方法。

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Finally and mysteriously, the plane disappeared without trace.

最后，飞机神秘地消失得无影无踪了。

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When the point moves along the plane curve , the trace curve of the point is called the evolute of the curve , denoted by, and is called the involute of the curve .

当点沿曲线移动时，相应的曲率中心的轨迹曲线称为曲线的渐屈线，而曲线称为曲线的渐伸线。

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He is thought to have headed home to the Comoros islands in the Indian Ocean immediately after the attacks, but as FBI agents tried to trace him there, he boarded a plane to the Gulf and disappeared without trace.

BBC: Profile: Fazul Abdullah Mohammed