#ellipses

7 messages · Page 1 of 1 (latest)

wooden girder
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Can someone please help me solve this? the product of the distances of the two focal points from a tangent is equal to the square of the semi-minor axis

elder kernelBOT
raven tinsel
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draw a picture

past marten
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If $P$ is the point on the ellipse and it has foci at $S$ and $S'$, you seek $PS\cdot PS'$. And, if $M$ and $M'$ are the feet of the perpendiculars from $P$ to the directrices, then $PS = ePM$, so the product you seek reduces to $e^2PM\cdot PM'$ where $e$ is the eccentricity. $PM$ and $PM'$ are easily calculated as horizontal distances.

wet kettleBOT
wooden girder
past marten
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draw a line through P which is perpendicular to the directrices. That line meets the directrices at points M and M'