Link 1 rotates about fixed axis F₁ and is connected by a sliding pair to slider 3. Link 2 rotates about fixed axis F₂ and is connected by sliding pair to slider 4. Flexible cord 5 is attached at points F₁ and F₂ and passes through an eye in pivot A, the turning pair connecting sliders 3 and 4. When link 1 rotates about axis F₁, point A describes ellipse q-q with its foci at points F₁ and F₂ and with the equation x²/a²+y²/b²=1 where a and b are the semiaxes of the ellipse. The length of cord b is equal to l=2a. By varying the distance c=sqrt(a²-b²) and the length l of cord 5, ellipses of various types can be traced.
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